Histiocyte-rich rhabdomyoblastic tumor: rhabdomyosarcoma, rhabdomyoma, or rhabdomyoblastic tumor of uncertain malignant potential? A histologically distinctive rhabdomyoblastic tumor in search of a place in the classification of skeletal muscle neoplasms.

Skeletal muscle tumors are traditionally classified as rhabdomyoma or rhabdomyosarcoma. We have identified an unusual adult rhabdomyoblastic tumor not clearly corresponding to a previously described variant of rhabdomyoma or rhabdomyosarcoma, characterized by a very striking proliferation of non-neoplastic histiocytes, obscuring the underlying tumor. Ten cases were identified in nine males and one female with a median age of 43 years (range 23-69 years). Tumors involved the deep soft tissues of the trunk (N = 4), lower limbs (N = 4), and neck (N = 2). Tumors were well-circumscribed, nodular masses, frequently surrounded by a fibrous capsule containing lymphoid aggregates and sometimes calcifications. Numerous foamy macrophages, multinucleated Touton-type giant cells, and sheets/fascicles of smaller, often spindled macrophages largely obscured the underlying desmin, MyoD1, and myogenin-positive rhabdomyoblastic tumor. Cases were wild type for MYOD1 and no other mutations or rearrangements characteristic of a known subtype of rhabdomyoma or rhabdomyosarcoma were identified. Two of four cases successfully analyzed using a next-generation sequencing panel of 170 common cancer-related genes harbored inactivating NF1 mutations. Next-generation sequencing showed no gene fusions. Clinical follow (nine patients; median 9 months; mean 23 months; range 3-124 months) showed all patients received wide excision; four patients also received adjuvant radiotherapy and none received chemotherapy. At the time of last follow-up, all patients were alive and without disease; no local recurrences or distant metastases occurred. We hypothesize that these unusual tumors represent rhabdomyoblastic tumors of uncertain malignant potential. Possibly over time they should be relegated to a new category of skeletal muscle tumors of intermediate (borderline) malignancy.

Fibrous hamartoma of infancy: a clinicopathologic study of 145 cases, including 2 with sarcomatous features.

Fibrous hamartoma of infancy is a rare soft tissue lesion of infants and young children with characteristic triphasic morphology, which typically occurs in the axilla and less commonly in other locations. We reviewed 145 cases of fibrous hamartoma of infancy from our consultation archives. Cases occurred in 106 males and 39 females (mean age-15 months; range-birth to 14 years), and involved both typical sites (eg, axilla/back/upper arm) (n=69) and unusual locations (n=76). Six were congenital. The tumors presented as subcutaneous masses and ranged from 0.4 to 17 cm (mean 3 cm). All displayed triphasic morphology, but varied widely in the relative percentages of fat, fibroblastic fascicles, and primitive mesenchyme. Hyalinized zones with cracking artifact, mimicking giant cell fibroblastoma, were present in a 44 (30%) of cases; however FISH for PDGFB gene rearrangement was negative in five tested cases. In addition to classical fibrous hamartoma of infancy, two lesions contained large sarcomatous-appearing foci with high cellularity, high nuclear grade, and brisk mitotic activity. One occurred in a 10-month-old female as a new mass in a congenital fibrous hamartoma of infancy; the other occurred as a leg mass in a 6-year-old male. ETV6 gene rearrangement was negative in the tumor from the 10-month-old female. Genomic microarray (OncoScan) showed normal molecular karyotype in eight tested cases, whereas the two tumors with sarcomatous features showed a hyperdiploid/near tetraploid molecular karyotype with copy neutral loss of heterozygosity of chromosomes 1p and 11p, and loss of 10p, chromosome 14, and a large portion of chromosome 22q (22q11.23q13.33), respectively. Follow-up (52 patients; range: 1-208 months, median: 8 months) showed only two local recurrences and no metastases. Extensive local disease in the 10-month-old female with sarcomatous-appearing fibrous hamartoma of infancy necessitated forequarter amputation. In summary, our study confirms the classic clinicopathologic features, including the triphasic morphologic appearance of most cases. In contrast to earlier studies, our series illustrates a broader histologic spectrum than previously appreciated, including its close resemblance to giant cell fibroblastoma in one quarter of cases and the rare presence of 'sarcomatous' areas, the latter providing evidence that these are complex neoplasms rather than hamartomas.

Superficial CD34-positive fibroblastic tumor: report of 18 cases of a distinctive low-grade mesenchymal neoplasm of intermediate (borderline) malignancy.

Fibroblastic mesenchymal tumors show a spectrum of biological behavior, from benign to fully malignant. We report our experience of two decades with a distinctive, previously undescribed low-grade fibroblastic tumor of the superficial soft tissues. Eighteen cases were identified within our consultation files, previously coded as 'low-grade sarcoma, not further classified' and 'malignant fibrous histiocytoma, low grade'. The tumors occurred in adults (median age 38 years, range 20-76 years) of either sex (10 males and 8 females), ranged in size from 1.5 to 10 cm (mean 4.1 cm), and were confined to the superficial soft tissues of the thigh (N=5), knee (N=2), and other sites. Histological features included a fascicular growth pattern of the neoplastic spindled cells with striking, often bizarre cellular pleomorphism and variably prominent nucleoli. Necrosis was seen in one case. All cases showed strong, diffuse CD34 positivity and 68% of tested cases demonstrated focal cytokeratin expression. Desmin, ERG, FLI-1, smooth muscle actin, and S100 protein were negative. TP53 overexpression was absent. Fluorescence in-situ hybridization studies for TGFBR3 and/or MGEA5 rearrangements were negative in all tested cases. Clinical follow-up was available in 13 patients (median duration of 24 months; range 1-104 months). Twelve of 13 patients had no disease recurrence. One patient had regional lymph node metastases, 7 years after incomplete excision of the primary tumor. All patients are currently alive and disease free. The unique clinicopathological features of superficial CD34-positive fibroblastic tumor define them as a novel subset of low-grade fibroblastic neoplasms, best considered to be of borderline malignancy.

Lymphatic-type "Angiosarcoma" With Prominent Lymphocytic Infiltrate.

We report 21 cases of a distinctive and unique vascular tumor which we propose to be a pure lymphatic-type angiosarcoma characterized by architectural and growth characteristics of angiosarcoma, cytologic, and immunohistochemical features of lymphatic differentiation, a prominent lymphocytic infiltrate, and variable nuclear grade. Patients included 12 males and 9 females with a median age of 65 years (range: 32 to 95 y). Tumors involved the head and neck (n=11), lower extremities (n=5), trunk (n=4), and upper extremity (n=1) and were located superficially in the dermis and/or subcutis. Tumors were designated "low grade" (n=10) when the nuclear grade was low, and vascular channel formation was evident throughout but with multilayering of endothelium within the vessels. Cases were designated "high grade" (n=11) when nuclei appeared higher grade with more rounded contours and prominent nucleoli and when solid areas predominated over vascular channel formation. A striking feature of both groups was the presence of a dense, lymphocytic infiltrate with occasional germinal center formation. All cases strongly and diffusely expressed at least 1 lymphatic marker (21/21) with podoplanin (17/19) and Prox-1 (11/11) more commonly expressed than LYVE-1 (5/10). No consistent molecular alteration was identified. Follow-up on 17 patients (median: 41 mo, mean: 54 mo) showed 10 patients were alive without disease, 5 were alive with disease, 1 died of other cause, and 1 died of disease. Local recurrence developed in 9 cases and metastasis in 2 cases, although neither correlated with grade as defined. On the basis of clinical follow-up to date, the natural history of lymphatic-type angiosarcoma appears to be more favorable than other forms of cutaneous angiosarcoma.

Intrasinusoidal Spread of Hepatic Epithelioid Hemangioendothelioma: Implications for the Diagnosis in Minimal Samples.

Epithelioid hemangioendothelioma (EHE) is an angiocentric tumor that, when arising in liver, is centered around hepatic/portal veins. However, EHE cells can also track along sinusoids, which is not well recognized or studied. We identified 18 cases of hepatic EHE and 6 nonhepatic EHEs. For all cases, we recorded EHE multifocality and maximum size. When tumor cells were identified apart from the main mass, we recorded their location, maximum distance from the main tumor, density per high-power field, and cytomorphology. Immunohistochemical staining for CAMTA1, ERG, and CAM5.2 was performed on all cases. Lesional cells were present apart from the main mass in 17 of 18 (94%) liver cases, always within sinusoids and occasionally (4/17, 24%) in central veins. They appeared intensely hyperchromatic with vaguely cerebriform nuclei and multinucleation in 6 (35%) of cases. CAMTA1 and ERG positivity was seen in all 17 cases. Two cases (12%) demonstrated focal CAM5.2 positivity. Sinusoidal EHE cells ranged from 0.1 to 0.8 cm away from the main tumor. There were no statistically significant associations between histologic findings and patient outcome. In the 6 nonhepatic cases, tumor cells did not extend beyond the main EHE. Lesional cells in hepatic EHE often extend beyond the main lesion into sinusoids, where they demonstrate an unusual, somewhat distinctive morphology. Care should be taken to identify such cells in limited biopsies; immunohistochemistry for CAMTA1, a specific and sensitive marker for EHE, can be confirmatory.

Sporadic cutaneous angiosarcomas: a proposal for risk stratification based on 69 cases.

Angiosarcomas have traditionally been considered high-grade lesions for which histologic features and grading have played no role in prognostication and, consequently, they have been excluded from the American Joint Committee on Cancer staging system. We have, therefore, analyzed 69 cutaneous angiosarcomas seen in consultation and not associated with lymphedema or prior radiation therapy to determine if a combination of histologic and clinical parameters could be used to differentiate indolent from aggressive tumors. The clinical features analyzed included patient age, location, size, depth, and focality of the lesion; the histologic features studied included pattern of growth (vasoformative vs. solid), nuclear grade (high vs. low), necrosis (present/absent), cell type (epithelioid or spindled), extent of inflammatory infiltrate (minimal vs. marked), and mitotic rate. Lesions occurred on the head/neck (49), extremities (15), and trunk (5) of adults (21 to 94 y) and predominated in males (41 males; 28 females). Tumors ranged in size from 0.3 to 15 cm (average 3.1 cm) and involved the papillary (n=9), reticular (n=16), or deep dermis/ subcutis (n=30). They could be predominantly vasoformative (n=28) to solid (greater than 50% solid, n=41). Most lesions were of high (n=65) as opposed to low (n=4) nuclear grade, were mitotically active (0 to 99/10 high power fields), and occasionally displayed necrosis (n=14) and epithelioid features (n=21). Inflammatory infiltrates were minimal in most cases. Follow-up information was obtained for all patients. Recurrences developed in 18 patients (26%) and metastasis in 15 (22%) to the following sites: lung (6), lymph node (7), liver (2), bone (2), and parotid gland (1). Forty-seven patients died (30 of disease) and 22 were alive at last known follow-up (range, 16 to 158 mo; mean, 65; median, 36). Five-year disease-specific survival was 48%. By univariate analysis only older age, anatomic site, necrosis, and epithelioid features correlated with increased mortality. Tumors were stratified into low (n=41) or high (n=28) risk groups based on necrosis and/or epithelioid features. By multivariable analysis, high-risk group (hazard ratio 4.07, P=0.0004) and age >70 (hazard ratio 2.79, P=0.012) were associated with increased mortality, and tumor depth (P=0.048) correlated with the risk of local recurrence. The high-risk group had a significantly worse prognosis than the low-risk group with 3-year survival of 24% and 77%, respectively. No patients with high-risk features survived 5 years. In conclusion, we report that a combination of clinical and histologic features allows stratification of angiosarcoma patients into 2 risk groups that are strongly associated with marked differences in clinical course. These features seem to diminish in importance with increased tumor size and are probably most useful in tumors less than 5 cm in maximum dimension.

The utility of fluorescence in situ hybridization (FISH) in the diagnosis of myxoid soft tissue neoplasms.

Diagnosing myxoid soft tissue neoplasms can be challenging because of overlapping histologic features. Distinct chromosomal translocations have been identified in several myxoid sarcomas, including t(12;16)(q13;p11) FUS-DDIT3 in myxoid liposarcoma, t(7;16)(q34;p11) FUS-CREB3L2 in low-grade fibromyxoid sarcoma, and t(9;22)(q31;q12) EWSR1-NR4A3 in extraskeletal myxoid chondrosarcoma. These recurrent chromosomal alterations are attractive targets for diagnostic studies. To that end, dual-color, break-apart fluorescence in situ hybridization (FISH) probes spanning the genomic regions of EWSR1 (22q12), DDIT3 (12q13), and FUS (16p11) (Vysis, Downer's Grove, IL) were evaluated in formalin-fixed, paraffin-embedded tissues from myxoid neoplasms, including intramuscular myxoma (n=10), myxoid liposarcoma (n=18), low-grade fibromyxoid sarcoma (n=10), extraskeletal myxoid chondrosarcoma (n=13), and myxofibrosarcoma (n=8). Of the myxoid liposarcomas, 18/18 cases had a rearrangement of the DDIT3 gene, with 17/18 (94.4%) showing both DDIT3 and FUS gene rearrangements. A FUS gene rearrangement was identified in 7/10 (70%) of low-grade fibromyxoid sarcomas, with no changes involving EWSR1 or DDIT3. An EWSR1 translocation was seen in 6/13 (46.2%) of extraskeletal myxoid chondrosarcomas, without changes in DDIT3 or FUS genes. The remaining neoplasms studied showed no rearrangements involving DDIT3, FUS, or EWSR1 genes. In conclusion, interphase FISH using DDIT3 and FUS probes identifies the characteristic translocation in myxoid liposarcoma. FUS and EWSR1 probes are useful in confirming the diagnosis of low-grade fibromyxoid sarcoma and extraskeletal myxoid chondrosarcoma, respectively. The specificity of the probes is documented as none of the non-translocation-associated myxoid tumors showed genomic abnormalities with the probes tested. FISH is capable of providing specific ancillary information useful in this often difficult differential diagnosis.

Subconjunctival herniated orbital fat: A benign adipocytic lesion that may mimic pleomorphic lipoma and atypical lipomatous tumor.

Prolapse of subconjunctival intraconal orbital fat is a rare cause of an intraorbital mass lesion. Over the past several years, we have seen a number of cases in which this prolapsed fat was confused pathologically with a neoplasm of adipocytic lineage, specifically pleomorphic lipoma and atypical lipomatous neoplasm (well-differentiated liposarcoma). We report the clinical, histopathologic, and immunohistochemical findings in 21 specimens from 17 patients, all of whom presented with prolapsed intraconal orbital fat. All specimens were routinely examined and processed for light microscopy. Immunohistochemistry for CD34, CD68, S100 protein, vimentin, alpha-smooth muscle actin, and Ki-67, and Giemsa, Masson trichrome, and alcian blue histochemical stains were performed. Clinical and follow-up information was extracted from a chart review. The mean age (+/-SD) of the patients was 65.6+/-11.9 years (range: 41 to 85 y); 2 were women and 15 were men. Subconjunctival prolapsed orbital fat was localized in the superotemporal quadrant or lateral canthus around the rectus muscle below the lacrimal gland. The lesions were unilateral in 10 and bilateral in 7 patients. No recurrence was clinically evident over a mean (+/-SD) follow-up time of 2.5+/-3.2 years (range: 1 mo to 13.5 y). Histopathologically, all specimens showed an admixture of mature fat, fibrous septae lacking hyperchromatic cells, adipocytes with intranuclear vacuoles (Lochkern cells), multinucleated giant cells with a wreathlike configuration of normochromatic nuclei (floret cells), and varying numbers of histiocytes, lymphocytes, plasma cells, and mast cells. "Control" sections of normal orbital fat showed occasional Lochkern cells but lacked floret cells. By immunohistochemistry, the floret cells expressed only CD34 and vimentin, whereas the Lochkern cells expressed CD34, S100 protein, and vimentin. We conclude that subconjunctival herniated orbital fat commonly contains multinucleated floretlike giant cells, fibrous septae, and Lochkern cells, features that may result in diagnostic confusion with pleomorphic lipoma and atypical lipomatous neoplasms. Importantly, specific diagnostic features, such as aggregates of bland spindled cells associated with wiry collagen, as seen in pleomorphic lipoma, and enlarged hyperchromatic cells within fibrous septae, as in atypical lipomatous neoplasms, are entirely absent in herniated orbital fat. Multinucleated floret cells present in prolapsed orbital fat likely represent a reactive phenomenon, as they are not present in normal orbital fat.

Heterotopic mesenteric ossification: a distinctive pseudosarcoma commonly associated with intestinal obstruction.

Heterotopic mesenteric ossification (HMO) is a rare intraabdominal bone-producing pseudosarcoma with fewer than 14 reported cases in the literature. We report our experience with 6 additional cases, all of which were referred to us with a diagnostic consideration of extraskeletal osteosarcoma (EO) or "sarcoma" and emphasize features which distinguish HMO from EO. Six intraabdominal lesions coded as "heterotopic mesenteric ossification," "ossifying pseudotumor," or "reactive myofibroblastic proliferation with ossification" were retrieved from our consultation files. Clinical follow-up information was obtained. Lesions occurred exclusively in males, with a mean patient age of 49 years (range, 22-72 years). The tumors occurred in the mesentery (N = 4), omentum (N = 1), or both (N = 1) and were preceded by significant abdominal surgery (4 cases) or trauma (1 case) in all but 1 case. Five patients presented with bowel obstruction and 1 with abdominal sepsis. Tumors were difficult to precisely measure; the mean size of the resection specimens was 11.8 cm (range, 3.5-20 cm). Grossly, the tumors resembled fat necrosis and often cut with a gritty sensation. Microscopically, all lesions demonstrated an exuberant, reactive (myo)fibroblastic proliferation resembling nodular fasciitis, with extensive hemorrhage and fat necrosis. All tumors produced abundant bone and osteoid, often "lace-like," and 2 contained cartilage. The proliferating (myo)fibroblasts, osteoblasts, and chondroblasts were mitotically active but cytologically bland. Follow-up (4 cases; mean, 47.3 months; range, 5-120 months) showed 3 patients alive without disease and 1 dead of unrelated causes. One case was recent. HMO is a distinct intraabdominal ossifying pseudotumor that typically occurs in males, almost always after surgery or abdominal trauma, and frequently presents with symptoms of intestinal obstruction. This clinical history, presence of clearly reactive zones resembling nodular fasciitis, thick osteoid, and absence of nuclear atypia, necrosis, and atypical mitotic figures allow the distinction of HMO from its most important morphologic mimic, EO.

Pseudosarcomatous myofibroblastic proliferations of the bladder: a clinicopathologic study of 42 cases.

Inflammatory pseudotumor or pseudosarcomatous fibromyxoid tumor and postoperative spindle cell nodule of the bladder are unusual lesions of uncertain pathogenesis which share overlapping, if not identical, histologic features. We present our experience with 42 cases, the largest series to date, to study the etio-pathogenesis, histologic features, biologic behavior and relationship to "inflammatory myofibroblastic tumor" of childhood. Patients ranged in age from 7 to 77 years (mean 47 y) and males predominated (3.2:1). Most patients presented with hematuria (31/42). Common associations were smoking (10/30) and previous instrumentation or surgery (9/42). The clinicopathologic features of patients having or not having prior instrumentation were identical. Grossly the lesions were polypoid or nodular and involved any portion of bladder wall, most commonly the dome (9/27) and measured 1 to 10 cm (mean 4 cm). They were composed of spindled and stellate cells arranged in a myxoid background with numerous inflammatory cells. Myxoid hypocellular areas were more pronounced near the mucosal surface with greater cellularity and a fascicular arrangement in the deep aspect of the lesion. "Atypical" features included mitotic activity (0 to 20/10 HPF; mean 2/10 HPF; median 1/10 HPF; none atypical), necrosis (22/42), and extension into muscularis propria (28/32) or perivesicular fat (3/8). Lesions were positive for cytokeratin (31/33), SMA (23/34), desmin (21/35), and Alk-1 protein (12/26). FISH confirmed the Alk-1 translocation in 4/6 cases. Treatment included transurethral resection (30/42), partial cystectomy (9/42), and total cystectomy (3/42). Initial diagnostic error resulted in radiotherapy and chemotherapy in 3 patients. Follow-up was available in 28 patients. (range 3 to 93 mo; median 25 mo). Three patients developed recurrences, but none had metastases. Because the clinicopathologic features of lesions associated with and without instrumentation were similar and inseparable, we believe they are essentially the same entity, and propose the term pseudosarcomatous myofibroblastic proliferation. The preponderance of evidence which includes the extravesical growth, local recurrence, and Alk-1 gene translocation in some cases suggests perhaps a neoplastic process with limited growth potential. Even in the face of atypical histologic features (muscle invasion and necrosis) the prognosis is excellent. Despite the Alk-1 gene translocation, there continues to be sufficient evidence for regarding these as distinct from the so-called inflammatory myofibroblastic tumor of childhood.

Epstein-Barr virus-associated smooth muscle tumors are distinctive mesenchymal tumors reflecting multiple infection events: a clinicopathologic and molecular analysis of 29 tumors from 19 patients.

Epstein-Barr virus-associated smooth muscle tumors (EBV-SMT) are rare lesions that occur in immunocompromised patients. Because they have not been fully characterized pathologically or at the molecular level, we have studied 29 tumors from 19 patients, the largest series to date. Cases coded as EBV-SMT were identified in 19 patients from consultation files and from the renal transplant database at Singapore General Hospital. EBV-SMT occurred in adults (mean age 39 years; range, 21-57 years) and predominantly affected males (12 male, 7 female). Causes of immunocompromise were renal transplantation (10), AIDS (8), and steroid therapy (1). Tumors were located in soft tissue (5), lung (5), liver (4), and miscellaneous sites (15). In 13 patients (68%), the tumors were multiple. Infection with EBV was confirmed in all cases by in situ hybridization for EBV early RNAs (EBER). EBV-SMT were typically well-differentiated smooth muscle tumors with little atypia and usually a low level of mitotic activity. Unlike classic leiomyosarcomas, they lacked significant pleomorphism but frequently displayed primitive round cell areas and prominent intratumoral T lymphocytes. No consistent relationship between histologic features and clinical outcome was noted. All expressed actin (29 of 29) and less frequently desmin (14 of 26). Multiple tumors in a given patient were clonally distinct as assessed by the long terminal repeat region of the virus, supporting the view that multifocal tumors arise from multiple infection events rather than from metastasis. Strain typing by analysis of the EBNA-3C gene confirmed the presence of EBV type 2. Two of four tumors assessed were positive for a 30-bp deletion in the LMP1 gene. EBV copy number per cell ranged greatly between patients and between tumors from the same patient. Follow-up information was available in 18 of 19 patients (mean, 25 months; range, 1-105 months). Fifteen patients were alive: 11 with disease and 4 without. Three patients died, 1 due to disease. We conclude that EBV-SMT are histologically distinct from classic soft tissue smooth muscle tumors, are not readily evaluated by means of conventional histologic criteria, and in the case of multifocal tumors are the result of multiple infection events rather than metastasis. EBV-2 can transform smooth muscle cells, independent of the presence of the LMP1 deletion associated with greater virulence.

Physician scientist research pathway leading to certification by the American Board of Pathology.

In 2014, the American Board of Pathology, in response to the pathology community, approved a physician scientist research pathway (PSRP). This brief report summarizes the history of and objectives for creating the physician scientist research pathway and the requirements of the American Board of Pathology for the certification of physician scientist research pathway trainees.

Physician Scientist Research Pathway Leading to Certification by the American Board of Pathology.

In 2014, the American Board of Pathology, in response to the pathology community, approved a physician scientist research pathway. This brief report summarizes the history of and objectives for creating the physician scientist research pathway and the requirements of the American Board of Pathology for the certification of physician scientist research pathway trainees.

Epithelioid Schwannomas: An Analysis of 58 Cases Including Atypical Variants.

The histologic features and outcome of 58 cases of epithelioid schwannoma were studied to determine the significance of atypical histologic features. Cases were retrieved from personal consultation files from 1999 to 2013. Patients (31 male and 26 female patients) ranged in age from 14 to 80 years (median, 38 y). Two patients had schwannomatosis 1. Tumors developed in the dermis/subcutis (n=56) or muscle (n=2) of the upper extremity (34.5%), lower extremity (34.5%), thorax/abdomen/back (18%), and less common anatomic locations including the scalp, neck, lip, and breast. They ranged in size from 0.25 to 4.5 cm (median, 2.0 cm). Typically circumscribed and surrounded by a perineurium, they comprised single or small groups of epithelioid schwann cells with a moderate amphophilic cytoplasm and occasional nuclear pseudoinclusions. Stroma varied from myxoid to hyalinized, often with thick-walled vessels (55 cases). Mitotic rate ranged from 0 to 9 mitoses/10 high-power field (HPF) (2.37 mm) in the most active areas (mean, 2 to 3 mitoses/10 HPFs). Thirteen cases (22%) were "atypical," defined by a high mitotic rate (≥3 mitoses per 10 HPFs) and nuclear size variation (≥3:1). All (56/56) expressed S100 protein; type IV collagen invested groups or individual cells (16/17). Melanoma markers were negative, except for melan A (1 case). Follow-up in 39 patients (median, 78 mo; range, 6 to 174 mo) indicated that 31 (79%) were alive without disease (including 9/13 atypical cases; median, 78 mo), 7 (18%) were alive with unknown status, and 1 patient had died of unrelated causes. One tumor recurred, but none metastasized. Epithelioid schwannomas, even those with atypical features, are benign and do not constitute a histologic continuum with epithelioid malignant peripheral nerve sheath tumors, which typically occur in deep soft tissues and have more anaplastic features.

MDM2 and CDK4 Immunohistochemistry: Should It Be Used in Problematic Differentiated Lipomatous Tumors?: A New Perspective.

Although most cases of atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) can be diagnosed solely on the basis of histologic features, those lacking diagnostic histologic features require ancillary studies for accurate classification. Fluorescent in situ hybridization (FISH) for amplification of MDM2 has been considered the gold standard for diagnosis in these situations. Immunostaining for MDM2 and/or CDK4 has been adopted as a surrogate method because of its high concordance rate with FISH and lower cost. However, studies examining the concordance of the 2 methods have been based preferentially on cases in which the diagnosis could be established histologically. No study has explored the concordance between the 2 methods in histologically ambiguous cases or in cases in which the diagnosis of ALT/WDL is not apparent after a review of all slides. To address this, we performed immunostaining for MDM2 and CDK4 on 183 well-differentiated lipomatous tumors that could not be diagnosed on purely histologic grounds and that were, therefore, subjected to FISH analysis. These included ALT/WDLs (n=56), lipomas (n=96), and lipoma variants (n=31). Staining for MDM2 and CDK4 was noted in 25/56 and 23/56 ALT/WDL, respectively, giving a sensitivity of 45% and 41% and a specificity of 98% and 92%. Staining was noted exclusively in the nuclei of atypical cells and not in the nuclei of adipocytes. Staining for MDM2 and CDK4 occurred in 2/125 and 10/117 benign lipomatous lesions, respectively. False-positive staining was equivalent in intensity to ALT/WDL. We conclude that MDM2 and CDK4 staining is a relatively insensitive method for diagnosing ALT/WDL in cases that are histologically ambiguous, as staining is restricted to neoplastic cells with atypia that are underrepresented in these cases. Therefore, in cases like ours that closely simulate clinical practice, FISH is the more reliable and cost-effective option.

TGFBR3 and MGEA5 rearrangements are much more common in "hybrid" hemosiderotic fibrolipomatous tumor-myxoinflammatory fibroblastic sarcomas than in classical myxoinflammatory fibroblastic sarcomas: a morphological and fluorescence in situ hybridization study.

Myxoinflammatory fibroblastic sarcoma (MIFS) is a rare low-grade sarcoma that most often involves the distal extremities of adults. Some MIFSs have been reported to show TGFBR3 and MGEA5 rearrangements. TGFBR3 and MGEA5 rearrangements have also been reported in hemosiderotic fibrolipomatous tumor (HFLT), in pleomorphic hyalinizing angiectatic tumor (PHAT), and in rare tumors allegedly showing features of both HFLT and MIFS (hybrid HFLT-MIFS). These findings have led to speculation that HFLT, MIFS, PHAT, and hybrid HFLT-MIFS are closely related; however, areas resembling HFLTs are only very rarely encountered in previous series of MIFSs. We studied classic examples of these tumors with the goal of clarifying the relationship between MIFS and HFLT-MIFS. Cases of MIFS (n=31), hybrid HFLT-MIFS (n=8), PHAT (n=2), HFLT (n=1), and undifferentiated pleomorphic sarcoma (n=4) were retrieved from our archives, and the diagnoses were verified by 5 soft tissue pathologists. Using previously validated break-apart fluorescence in situ hybridization probes, we analyzed for TGFBR3 and MGEA5 rearrangements. Only 2 of 31 MIFSs harbored MGEA5 rearrangements; all lacked TGFBR3 rearrangements. Six of 8 hybrid HFLT-MIFSs harbored rearrangements of TGFBR3 and/or MGEA5. Both PHATs were positive for rearrangements of TGFBR3 and/or MGEA5. The HFLT was positive for rearrangements of both TGFBR3 and MGEA5. All undifferentiated pleomorphic sarcomas with focal myxoid change were negative. We conclude that (1) TGFBR3 and/or MGEA5 rearrangements are much more common in hybrid HFLT-MIFSs than in classic MIFSs, (2) HFLTs and MIFSs may be unrelated lesions, and (3) hybrid HFLT-MIFSs most likely represent HFLTs with sarcomatous progression, rather than tumors strictly related to classic MIFSs.

Perivascular epithelioid cell neoplasms of soft tissue and gynecologic origin: a clinicopathologic study of 26 cases and review of the literature.

PEComas, occasionally associated with the tuberous sclerosis complex, are defined by the presence of perivascular epithelioid cells that coexpress muscle and melanocytic markers. This family of tumors includes angiomyolipoma (AML), clear cell sugar tumor of the lung (CCST), lymphangioleiomyomatosis (LAM), and very rare tumors in other locations. Because non-AML/non-LAM PEComas are extremely rare and their natural history and prognostic features undefined, we present our experience with 26 PEComas of soft tissue and the gynecologic tract, the largest series to date. We also performed a detailed review of the literature, with special attention to features predictive of clinical behavior. All PEComas exclusive of AML and LAM were retrieved from our consultation files. Immunohistochemistry for pan-cytokeratin (CK), S-100 protein, smooth muscle actins (SMA), desmin, vimentin, HMB45, Melan-A, microphthalmia transcription factor (MiTF), TFE3, CD117, and CD34 was performed. Clinical follow-up information was obtained. Fisher's exact test was performed. The median patient age was 46 years (range, 15-97 years); there was a marked female predominance (22 females, 4 males). Sites of involvement included the omentum or mesentery (6 cases), uterus (4 cases), pelvic soft tissues (3 cases), abdominal wall (2 cases), uterine cervix (2 cases), and vagina, retroperitoneum, thigh, falciform ligament, scalp, broad ligament, forearm, shoulder, and neck (1 case each). The tumors ranged from 1.6 to 29 cm in size (median, 7.8 cm). Tumors were epithelioid (N = 9), spindled (N = 7), or mixed (N = 10). Multinucleated giant cells were present in 18 cases. High nuclear grade was noted in 10 cases, high cellularity in 7 cases, necrosis in 8 cases, and vascular invasion in 3 cases. Mitotic activity was 0 to 50 mitotic figures (MF)/50 high power fields (HPF) (median, 0 MF/50 HPF) with atypical MF in 6 cases. IHC results were: SMA (20/25), desmin (8/22), HMB45 (22/24), Melan-A (13/18), MITF (9/18), S-100 protein (8/24), CK (3/23), vimentin (12/14), TFE3 (5/17), c-kit (1/20), and CD34 (0/7). Clinical follow-up (24 of 26 patients, 92%; median, 30 months; range, 10-84 months) showed 3 local recurrences and 5 distant metastases. At last available clinical follow-up, 2 patients (8%) were dead of disease, 4 patients (17%) were alive with metastatic or unresectable local disease, and 18 patients (75%) were alive with no evidence of disease. No patient in our series had a history of tuberous sclerosis complex. Recurrence and/or metastasis was strongly associated tumor size > median size (8 cm), mitotic activity greater than 1/50 HPF, and necrosis. We conclude that PEComas of soft tissue and gynecologic origin may be classified as "benign," "of uncertain malignant potential," or "malignant." Small PEComas without any worrisome histologic features are most likely benign. PEComas with nuclear pleomorphism alone ("symplastic") and large PEComas without other worrisome features have uncertain malignant potential. PEComas with two or more worrisome histologic features should be considered malignant. Occasional PEComas express unusual markers, such as S-100 protein, desmin, and rarely CK. The role of TFE3 in PEComas should be further studied.

Morphologic and immunophenotypic diversity in Ewing family tumors: a study of 66 genetically confirmed cases.

More than 85% of Ewing sarcoma/primitive neuroectodermal tumor (ES/PNET), or "Ewing family of tumors" (EFTs), have the translocation, t (11;22) (q24;q12), with others having variant translocations. Identification of these by cytogenetic and/or molecular genetic techniques is specific for EFT and is increasingly recognized as the "gold standard" for diagnosis. However, these techniques are not universally available. We therefore studied a large group of genetically confirmed EFTs to more completely understand the morphologic and immunophenotypic spectrum of this rare sarcoma. Sixty-six cytogenetically, FISH or RT-PCR proven-EFTs were retrieved. In 56 cases, immunohistochemistry (IHC) was performed for pan-cytokeratins (PanCK), high molecular weight cytokeratins (HMWCK), desmin (DES), CD99, CD117, and FLI1 protein using heat-induced epitope retrieval and the Dako Envision system. The cases arose chiefly in children and young adults (median 18 years; range, 3-65 years) of both sexes (male, 32; female, 31; unknown, 3) in a variety of bone (N = 39) and soft tissue (N = 27) sites. Histologically, 46 cases (73%) showed only typical features of ES, 9 cases (16%) showed features of PNET, 3 cases (5%) showed "adamantinoma-like" features, 3 cases (5%) corresponded to "atypical Ewing sarcoma," 3 cases (5%) showed principally intersecting fascicles of spindled cells, and 2 cases had abundant hyalinized matrix. IHC results were as follows: PanCK (18 of 56, 32%), HMWCK (3 of 55, 5%), DES (1 of 56, 2%), CD99 (52 of 52, 100%), CD117 (13 of 54, 24%), and FLI1 (44 of 47, 94%). HMWCK was expressed only in "adamantinoma-like" EFTs, none of which expressed DES. In conclusion, most, but not all, EFTs can be accurately diagnosed using time-honored morphologic criteria and ancillary immunohistochemistry. However, genetic confirmation remains essential for the diagnosis of unusual morphologic variants of EFT, including "adamantinoma-like," spindled, sclerosing, and clear cell/anaplastic variants. Therefore, to exclude or confirm the diagnosis of Ewing's sarcoma in round cell sarcomas having a variety of patterns but not specifically conforming to a tumor of known lineage (eg, rhabdomyosarcoma), cytogenetics, and/or molecular analysis is required.

Expression of Wilms tumor 1 gene distinguishes vascular malformations from proliferative endothelial lesions.

BACKGROUND: Vascular malformations and hemangiomas, which are endothelial lesions of childhood, may result in considerable morbidity because they can cause discomfort and functional impairment and have a negative affect on the patient's appearance. Although vascular malformations may initially appear very similar to hemangiomas, they have distinct clinical courses. Infantile hemangiomas progress through 3 stages: proliferative, involuting, and involuted. The proliferative phase is characterized by clinical growth. Once hemangiomas reach their maximum size, they begin to regress or involute. Histologically, this stage is characterized by endothelial apoptosis. Finally, the involuted stage of the hemangioma occurs when the original lesion is replaced by a connective tissue remnant. In contrast to hemangiomas, vascular malformations do not involute but continue to enlarge as the patient grows. OBSERVATIONS: The biochemical differences between hemangiomas, which involute, and vascular malformations, which do not involute, are not well understood. We found that the transcription factor encoded by the Wilms tumor 1 (WT1) gene is expressed in the endothelium of hemangiomas but not in vascular malformations. CONCLUSIONS: Defects in WT1 signaling may underlie the inability of malformation endothelial cells to undergo physiologic apoptosis and remodeling. The availability of WT1 staining in hospital laboratories may allow the clinician to distinguish hemangiomas from vascular malformations and thus to give appropriate therapy to the patient.

Soft tissue sarcomas of adults: state of the translational science.

Sarcomas--like leukemias, which are also mesodermal malignancies--carry biological significance disproportionate to their clinical frequency. Identification of mutations and translocations associated with these tumors has illuminated aberrant signaling pathways that cause these diseases, determine their behavior, and are therapeutic targets. Activated receptor-associated tyrosine kinase c-kit, mutated in most gastrointestinal stromal tumors, has proven a clinically effective target for enzyme inhibition. A translocation involving a single gene family, consisting of EWS and related genes, has been identified in five different sarcomas, and its chimeric protein products could prove similarly amenable to inhibitors. Resolution of the histopathological complexity is being aided by data from molecular and chromosomal characterization. Improvements in imaging, definition of prognostic factors, and surgical and radiotherapeutic treatment have resulted in improved local control. Continued progress will depend on further adapting the rapidly evolving technologies of genomics and proteomics. It will also depend upon accurate histopathological diagnosis based on validated reagents and consistent methodologies applied to adequate tissue samples derived from patients with complete clinical data. Finally, multicenter, coordinated trials, such as those that occurred with assessment of imatinib mesylate in metastatic gastrointestinal stromal tumors, will assure the most rapid reductions in morbidity and mortality.