Cutaneous crystal storing histiocytosis: A case series with review of literature.

Crystal-storing histiocytosis (CSH) is a rare condition in which crystals accumulate in the cytoplasm of histiocytes and is usually associated with a lymphoplasmacytic neoplasm. Cutaneous CSH is extraordinarily rare and limited to case reports in the literature. We report two cases of this disease with cutaneous involvement. Case 1 was a 65-year-old male with a 4-month history of a pruritic eruption that started as a solitary pink to skin-colored indurated plaque on the anterior neck before progressing to involve the whole neck, chest wall, and face. Case 2 was a 54-year-old woman with a history of unspecified "lymphoma" who presented with a soft nodule on the forearm. Biopsies from both cases had similar findings and showed a proliferation of epithelioid cells with pink cytoplasm and intracellular crystalline structures infiltrating the dermis and subcutaneous fat. In the first case, the cells were positive for CD43, CD45, CD68, and IgG kappa, and in the second case, the crystals were positive for IgG lambda. Based on these findings, the patients were diagnosed with cutaneous CSH. We highlight this rare diagnosis and the importance of investigating an underlying lymphoplasmacytic neoplasm.

MED15::ATF1-Rearranged Tumor: A Novel Cutaneous Tumor With Melanocytic Differentiation.

We recently described novel dermal tumors with melanocytic differentiation and morphologic and biological similarities to cutaneous clear cell sarcoma, including CRTC1::TRIM11 cutaneous tumor, and clear cell tumors with melanocytic differentiation and either ACTIN::MITF or MITF::CREM. Here, we describe a series of 3 patients presenting with tumors reminiscent of CRTC1::TRIM11 cutaneous tumor, found to demonstrate a novel MED15::ATF1 fusion. All 3 patients were children (5-16 years old). Primary excision of case 1 showed a circumscribed wedge-shaped silhouette with peripheral intercalation into collagen fibers and scattered lymphoid aggregates. All 3 tumors abutted the epidermis; one showed a junctional component. Tumors were highly cellular and comprised of monomorphic, oval-to-round epithelioid cells arranged in vague nests and short fascicles in variably fibrotic stroma. Mitotic rate was high (hotspot 6-12/mm2), without atypical mitoses. Necrosis was focally present in case 3. All cases showed strong, diffuse nuclear staining for SOX10 and MITF (2/2) but showed variable expression for S100 protein (1/3) and other melanocytic markers-Melan-A (focal in 2/3), HMB45 (focal in 1/3), and Pan-Melanoma (patchy in 1/1). Whole-exome RNA sequencing demonstrated a MED15::ATF1 fusion without any other notable alterations. Cases 1 and 2 were completely excised without recurrence (12 months). Case 3 developed a grossly apparent regional lymph node spread shortly after primary biopsy. The patient was treated with wide excision, radiation, cervical lymph node dissection (4/46 with >75% lymph node replacement), and neoadjuvant and adjuvant nivolumab (alive without disease at cycle 11). This series is presented to aid in future diagnosis of this novel dermal tumor with melanocytic differentiation and emphasize the potential for aggressive biologic behavior, which should be considered in patient management planning.

Novel EWSR1::GFI1B gene fusion in angiofibroma of soft tissue.

AIMS: Angiofibroma of soft tissue is a benign soft tissue tumour characterised by bland spindle cells and a distinct branching vascular network. The majority of soft tissue angiofibromas harbour AHRR::NCOA2 gene fusions. Here we present three cases of EWSR1::GFI1B-fused soft tissue tumours that are morphologically most reminiscent of soft tissue angiofibroma. METHODS AND RESULTS: All three cases presented in male patients with an age range of 35-78 years (median = 54 years). Two cases presented as subcutaneous nodules on the trunk (posterior neck and chest wall); one was an intramuscular foot mass. The tumours were unencapsulated nodules with infiltrative margins ranging from 2.2 to 3.4 cm in greatest dimension. Histologically, the tumours contained uniformly bland fibroblastic spindle cells with ovoid to fusiform nuclei and delicate cytoplasmic processes embedded in a myxoid to myxocollagenous stroma. All three cases were characterised by a thin-walled, branching vascular network evenly distributed throughout the tumour. Overt cytological atypia or conspicuous mitotic activity was absent. The spindle cells had an essentially null immunophenotype. By targeted RNA sequencing, an in-frame gene fusion between EWSR1 exons 1-7 and GFI1B exons 6-11 or 7-11 was detected in all three cases. The tumours were marginally excised. For all three cases, there were no documented local recurrence or distant metastases during a limited follow-up period of 6-10 months. CONCLUSIONS: We propose that EWSR1::GFI1B may represent a novel fusion variant of soft tissue angiofibroma.

Myxofibrosarcoma in adolescents and young adults: a clinicopathologic study of 17 cases.

Myxofibrosarcoma is a locally aggressive sarcoma that characteristically arises in the extremities of older patients. Cases arising at a younger age are rare, leading to diagnostic challenges. Our aim was to study the clinicopathologic features of myxofibrosarcoma in patients aged ≤40 years. Cases of myxofibrosarcoma and myxoid malignant fibrous histiocytoma arising in patients aged ≤40 years with clinical follow-up were collected from multiple institutions. Hematoxylin and eosin slides were evaluated for mitoses, necrosis, and epithelioid areas. Seventeen cases were identified (13 females, 4 males; 16-39 years; median 32 years), tumors ranged from 2.2 to 34 cm (median 4.1 cm). Anatomic sites included proximal extremity (9), distal extremity (4), trunk (1), and head/neck (3). Ten were superficial, and 6 were deep-seated. Three cases were predominantly epithelioid. In untreated resection specimens, 6 were FNCLCC grade 1, 4 grade 2, and 2 grade 3. Follow-up (6-204 months, median 36 months) revealed that 2 patients experienced local recurrences, 1 distant metastasis, and 2 patients both. The 5-year overall survival (OS) and event-free survival (EFS) were 84% and 55.9%, respectively. Tumor depth and necrosis were correlated with inferior OS (P = .025, P = .005), while tumor depth was also associated with worse EFS (P = <.001). We conclude that myxofibrosarcomas arising in adolescents and young adults show similar behavior compared to their older adult counterparts. Tumor depth and necrosis are poor prognostic factors in myxofibrosarcoma in this age group. Awareness that myxofibrosarcoma can rarely present in this population is important for accurate diagnosis.

Subcutaneous Leiomyosarcoma: An Aggressive Malignancy Portending a Significant Risk of Metastasis and Death.

Subcutaneous leiomyosarcoma (LMS) is a rare, poorly understood variant. The current literature on the subject is sparse, consisting of isolated case reports and small clinicopathologic studies compromised by the inclusion of both its more common and indolent counterpart, cutaneous LMS (atypical intradermal smooth muscle neoplasm), as well as highly aggressive deep-seated tumors. Thus, precise clinicopathologic characterization is limited. Cases of subcutaneous LMS reviewed at the University of Michigan and Cleveland Clinic from 1994 to 2022 were included in this retrospective study. A total of 39 cases were identified. The mean age was 61 years, and the cohort was predominantly male (23/39; 59%). Tumors averaged 4.2 cm and most commonly arose on the extremities (32/39; 82%). The majority (38/39; 97%) were diagnosed at an early pathologic stage (pT1 or pT2). Histopathologically, most tumors were well-circumscribed and were assigned a Fédération Nationale des Centers de Lutte Contre le Cancer grade of either 1 or 2 (24/39; 62%). The majority (22/39; 56%) appeared to arise in association with a blood vessel. Of the 36 cases with accessible clinical data and follow-up (mean 34 mo, range 0 to 94 mo), 12 (33%) were noted to have metastasized, with the lung representing the most common anatomic location. One case recurred locally. Six of 36 patients (17%) died from the disease at an average of 47 months after diagnosis (range 16 to 94 mo). Metastasis or death from disease was significantly associated with the Fédération Nationale des Centers de Lutte Contre le Cancer grade ( P =0.0015), the presence of necrosis ( P =0.032), tumor size ( P =0.049), and AJCC tumor stage ( P =0.036). These data demonstrate that subcutaneous LMS are more aggressive than dermal-based tumors and have a prognosis akin to that of deep-seated LMS.

Keratin-positive giant cell-rich tumors of soft tissue with HMGA2::NCOR2 fusions.

BACKGROUND: Giant cell tumor of soft tissue (GCT-ST) is a rare soft tissue neoplasm that is morphologically similar to but genetically distinct from giant cell tumor of bone. A novel keratin-positive GCT-ST (KPGCT-ST) harboring HMGA2::NCOR2 fusions was recently discovered. Fewer than 30 cases have been described; herein is reported an additional seven. METHODS: Cases diagnosed as GCT-ST were retrieved from institutional archives and consultation files. The histopathologic characteristics were assessed, and the electronic medical record was reviewed. RESULTS: Seven tumors were identified in six women and one man with a median age of 23 years. All patients underwent excision; no recurrences or metastases were noted during a median follow-up period of 7 months. Histopathologically, the tumors were characterized by a multinodular proliferation of keratin-positive mononuclear cells with evenly admixed osteoclast-like giant cells and absent neoplastic bone. A fibrous capsule with lymphoid cuffing was frequently seen. Foamy macrophages, inflammation, hemorrhage, and hemosiderin were variably present. The HMGA2::NCOR2 fusion was detected in all cases. CONCLUSIONS: Our findings support previously reported hypotheses that KPGCT-ST is a spectrum of the same entity as the recently described xanthogranulomatous epithelial tumor. Although follow-up data are limited, to date, KPGCT-ST appears to follow an indolent course.

Novel NONO::TFE3 fusion and ALK co-expression identified in a subset of cutaneous microcystic/reticular schwannoma.

Microcystic/reticular schwannoma (MRS) is a benign variant of schwannoma with a predilection for the gastrointestinal tract and skin. To date, genetic characterization of this tumor is limited. Prompted by the identification of TFE3::NONO fusion and ALK overexpression in an index case of MRS, a cohort of tumors was collected from institutional and consultation archives of two institutions. Next-generation sequencing (NGS), TFE3 fluorescence in situ hybridization (FISH), and TFE3 and ALK immunohistochemistry were performed, while clinicopathologic variables were documented. Eighteen MRS cases were identified (35 to 85 years) arising in the skin (n=8), gastrointestinal tract (n=5), adrenal gland (n=3), abdominal wall (n=1), and unknown site (n=1). Tumors showed a circumscribed to multinodular to plexiform low-power architecture with variable amounts of microcystic/reticular and solid schwannian components. Mitotic figures were scarce (0-1/10 HPFs), and atypia was absent. S100 protein and/or SOX10 immunoreactivity was noted in the microcystic/reticular and schwannian areas of all cases. NGS performed on two cutaneous tumors yielded NONO exon 12 fusion with TFE3 exon 4, and these lesions also showed HMB45 and ALK expression. Two additional cases showed ALK expression (1 weak), while a third was positive for TFE3, but these cases failed to show ALK or TFE3 rearrangement by FISH/NGS. There were no morphologic variables that correlated with the presence of NONO::TFE3. We identified a subset of microcystic/reticular schwannomas with NONO::TFE3 fusions and ALK co-expression, adding to the cohort of mesenchymal neoplasms that show ALK overexpression without rearrangement of the ALK gene.

Nipple Adenoma: Clinicopathologic Characterization of 50 Cases.

Nipple adenoma (NA) is a rare, benign proliferation of the nipple ducts. It may be clinically mistaken for Paget disease or squamous cell carcinoma; thus, microscopic evaluation is paramount. A large case series of NA has not been undertaken since the 1980s. Therefore, we undertook this study to evaluate the clinicopathologic characteristics of NA, emphasizing differential diagnoses and follow-up data. We retrieved 50 cases from our in-house archives or consultation files between 2003 and 2022. Available slides were reviewed, and clinical data and follow-up information were obtained. Cases must have exhibited a dense ductal proliferation in the breast tissue with proximity to the nipple epidermis. All patients were women; median age was 56 years. In all, 68% of patients were symptomatic; 53% demonstrated a skin growth. Overall, 67% were excised completely, either primarily (33%) or via re-excision after biopsy (33%). Four histologic patterns were noted: adenosis (dense proliferation of small-to-medium ducts); large duct (medium-to-large caliber ducts); papillary-like (frond-like architecture with branching, slit-like lumens); and pseudoinfiltrative (ducts squished and distorted by dense stromal fibrosis). Follow-up in 44 patients (88%) with a median time of 66 months showed no evidence of recurrence. NA demonstrates a wide spectrum of histopathologic variation. Subtyping of this entity is unlikely to be clinically relevant. Differentiation from invasive carcinoma or other histologic mimics (syringocystadenoma papilliferum, syringomatous adenoma) may be difficult. Simple excision is curative, and recurrence is rare. A definitive link to invasive carcinoma has not been established.

Pseudoxanthoma-elasticum-like changes on the soft palate.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive genetic disorder characterized by aberrant fragmentation and calcification of elastic fibers, leading to characteristic cutaneous, ophthalmic, and cardiovascular manifestations. PXE demonstrates significant phenotypic variability; involvement of the oral mucosa may be the only clue to the diagnosis. Reports on mucous membrane involvement in PXE are scarce. Here, we present a case of PXE-like changes in the oral cavity. A 70-year-old male patient presented with a painless leukoplakic lesion on the soft palate. Biopsy revealed numerous degenerated fibers in the lamina propria. Verhoeff-van Gieson and von Kossa staining confirmed their identity as calcified elastic fibers. A histopathological diagnosis of PXE-like changes was made; the patient was referred to ophthalmology where angioid streaks were visualized fundoscopically. PXE-like changes in the absence of the characteristic genetic mutation have also been reported with or without systemic manifestations. Furthermore, PXE-like changes have been reported in up to 10% of oral biopsy specimens undertaken without clinical suspicion for PXE. Therefore, the significance of such changes in isolation is unclear. Clinicians and pathologists should be aware of the potential oral manifestations of PXE to facilitate prompt diagnosis and subspecialist referral.

Myoepithelioma, myoepithelioma-like, and chondroid soft-tissue tumors arising at acral sites: a review.

Myoepithelial neoplasms comprise a histologically and immunophenotypically diverse spectrum of entities. The following review is a comprehensive summary of acral lesions demonstrating myoepithelial-like and chondroid histomorphology, as well as recently described mimics that are diagnostically challenging to distinguish. The salient clinicopathologic, immunophenotypic, and molecular features of each entity are described.

Narrative Review of the Pathogenesis of Stasis Dermatitis: An Inflammatory Skin Manifestation of Venous Hypertension.

INTRODUCTION: Stasis dermatitis (SD), also known as venous dermatitis, is a form of inflammatory dermatitis of the lower extremities that typically occurs in older individuals and represents a cutaneous manifestation of venous hypertension. Venous hypertension (also known as sustained ambulatory venous pressure) is most often due to retrograde blood flow, which occurs due to calf muscle pump failure. This failure is most commonly secondary to incompetent venous valves, valve destruction, or obstruction of the venous system. Many of the common symptoms associated with SD are caused by inflammatory processes. METHODS: This review summarizes the pathogenesis and key role of inflammation in SD by reviewing inflammatory biomarkers associated with SD. The literature was selected though a high-level PubMed search focusing on keywords relating to inflammation associated with SD. RESULTS: Venous reflux at the lower extremities causes venous hypertension, which leads to chronic venous insufficiency. High venous pressure due to venous hypertension promotes the local accumulation and extravasation of inflammatory cells across the vascular endothelium. Leukocyte trapping in the microcirculation and perivascular space is associated with trophic skin changes. Cell adhesion molecules are linked with the perpetuated influx of activated leukocytes into inflammatory sites. Here, inflammatory cells may influence the remodeling of the extracellular matrix by inducing the secretion of proteinases such as matrix metalloproteinases (MMPs). The increased expression of MMPs is associated with the formation of venous leg ulcers and lesions. Phosphodiesterase 4 activity has also been shown to be elevated in individuals with inflammatory dermatoses compared to healthy individuals. DISCUSSION: Because inflammation is a key driver of the signs and symptoms of SD, several of the highlighted biomarkers of inflammation represent potential opportunities to target and interrupt molecular pathways of cutaneous inflammation and, therefore, remediate the signs and symptoms of SD. CONCLUSION: Understanding the pathogenesis of SD may help clinicians identify drivers of inflammation to use as potential targets for the development of new treatment options.

Stasis dermatitis is a skin disease that affects the legs, most often of older people, with chronic venous insufficiency. Chronic venous insufficiency is when veins cannot return blood from the legs back to the heart. This leads to high blood pressure in veins and causes blood in those veins to flow backwards. If stasis dermatitis is left untreated, complications, including skin ulcers, can result. Other skin symptoms of stasis dermatitis include itchiness, scaling, and discoloration. Such skin symptoms can have a negative effect on a person's quality of life. Inflammation that lasts a long time is likely the main link between the skin changes seen in people with stasis dermatitis and the increased pressure in leg veins. Several molecules are associated with the inflammation observed in stasis dermatitis, including white blood cells, matrix metalloproteinases, phosphodiesterase 4, and interleukin-31. Treatment for stasis dermatitis should focus both on the underlying chronic venous insufficiency and the associated skin issues. Identifying inflammatory markers and pathways could help treat the signs and symptoms associated with stasis dermatitis, including the skin symptoms.

Paratesticular Dedifferentiated Liposarcoma with Epithelioid Features: A Diagnostic Pitfall.

Well-differentiated/dedifferentiated liposarcoma (WDLPS/DDLPS) represent a significant number of sarcomas arising within the paratesticular region. DDLPS is notorious for a broad histologic spectrum, but epithelioid morphology is rare. Herein, we describe a unique case of paratesticular DDLPS with prominent epithelioid features and molecular confirmation. The patient is 71-year-old-male who presented with multiple paratesticular masses. Morphologic review of the resection specimen revealed a biphasic adipocytic neoplasm consistent with DDLPS. Additionally, epithelioid foci with acinar and nested architecture and focal keratin expression were noted. These areas raised the possibility of a secondary neoplasm including sex cord stromal tumor, germ cell tumor, and paraganglioma. However, MDM2 immunohistochemistry and FISH showed these areas to express MDM2 and exhibit MDM2 amplification, respectively, confirming that they represented a component of DDLPS. This case further highlights the morphologic diversity of DDLPS as well as the utility of MDM2 studies.

Rhabdomyosarcoma Arising in an Old Rhytidectomy Scar.

OBJECTIVE: The clinical evaluation and management of an adult with head and neck rhabdomyosarcoma is explored to delineate the diagnostic challenge posed by soft-tissue sarcomas bordering scar tissue. CASE REPORT: A 59 year old female presents with persistent, evolving paresthesia and burning in the right posterior neck, which was found to be in close proximity to a well-healed rhytidectomy scar. Serial biopsies were non-diagnostic. Six months after initial presentation, rhabdomyosarcoma was diagnosed subsequent to histopathological and immunohistochemistry analysis. A wide local excision with posterolateral neck dissection was performed. CONCLUSION: A high index of suspicion for soft-tissue sarcoma should be maintained for patients with persistent soft-tissue lesions, especially in areas of scarred tissue, who present with new-onset neurological symptoms in the context of nondiagnostic biopsies.

Combined utility of p16 and BRAF V600E in the evaluation of spitzoid tumors: Superiority to PRAME and correlation with FISH.

BACKGROUND: Spitzoid melanocytic neoplasms are diagnostically challenging; criteria for malignancy continue to evolve. The ability to predict chromosomal abnormalities with immunohistochemistry (IHC) could help select cases requiring chromosomal evaluation. METHODS: Fluorescence in situ hybridization (FISH)-tested spitzoid neoplasms at our institution (2013-2021) were reviewed. p16, BRAF V600E, and preferentially expressed antigen in melanoma (PRAME) IHC results were correlated with FISH. RESULTS: A total of 174 cases (1.9F:1M, median age 28 years; range, 5 months-74 years) were included; final diagnoses: Spitz nevus (11%), atypical Spitz tumor (47%), spitzoid dysplastic nevus (9%), and spitzoid melanoma (32%). Sixty (34%) were FISH positive, most commonly with absolute 6p25 gain (RREB1 > 2). Dermal mitotic count was the only clinicopathologic predictor of FISH. Among IHC-stained cases, p16 was lost in 55 of 134 cases (41%); loss correlated with FISH positive (p < 0.001, Fisher exact test). BRAF V600E (14/88, 16%) and PRAME (15/56, 27%) expression did not correlate with FISH alone (p = 0.242 and p = 0.359, respectively, Fisher exact test). When examined together, however, p16-retained/BRAF V600E-negative lesions had low FISH-positive rates (5/37, 14%; 4/37, 11% not counting isolated MYB loss); all other marker combinations had high rates (56%-75% of cases; p < 0.001). CONCLUSIONS: p16/BRAF V600E IHC predicts FISH results. "Low-risk" lesions (p16+ /BRAF V600E- ) uncommonly have meaningful FISH abnormalities (11%). PRAME may have limited utility in this setting.

Superficial low-grade fibromyxoid sarcoma.

BACKGROUND: Low-grade fibromyxoid sarcoma (LGFMS) typically involves deep soft tissue (beneath the fascia) of the proximal extremities and trunk. Long-term follow-up has shown a high rate of local recurrence, metastasis, and death. To the best of our knowledge, there is only one previous large series focusing on superficial LGFMS suggesting superficial tumors are disproportionately more common in children and may have a better prognosis. Our study's primary goals are to confirm these findings and increase general awareness that LGFMS may arise in superficial soft tissue. METHODS: We retrieved our cases of superficial LGFMS diagnosed between 2008 and 2020. Available slides were reviewed, and clinical data and follow-up information were obtained. RESULTS: The patients included nine males and 14 females with a median age of 29 years; eight (35%) were children (<18 years) and five (22%) were young adults (18-30 years). The majority involved the lower extremities (65%). The tumors were primarily centered in the subcutis (91%) and dermis (9%). Microscopically, they had typical features of LGFMS with alternating fibrous and myxoid zones composed of bland, slightly hyperchromatic spindled cells. All were positive for MUC4 by immunohistochemistry and/or FUS rearrangement by FISH. Follow-up on 14 cases ranged from 11 to 148 months (median 61 months) with no evidence of recurrences or distant metastases. CONCLUSIONS: Compared to conventional deep-seated counterparts, superficial LGFMS is more likely to occur in the extremities of children and young adults and may have a better clinical outcome. Further studies with longer follow-up will likely help support these findings.

Myxoid Pseudotumor Involving the Renal Sinus: Clinicopathologic Study of 33 Cases Supporting a Distinct Benign Non-neoplastic Lesion.

We describe 33 cases of myxoid pseudotumor involving the renal sinus from 31 patients. Patients included 21 men and 10 women, ages 30 to 95 years. Twenty-seven cases (82%) had an associated malignancy, including urothelial carcinoma of the renal pelvis (22 cases), clear cell renal cell carcinoma (3 cases), urothelial carcinoma of the bladder (1 case), and poorly differentiated carcinoma of uncertain lineage (1 case). The remaining 6 (18%) had no associated malignancy and included 3 nephrectomies for ureteral stricture, 2 ureteropelvic junction repairs, and 1 resection of a "periureteral mass" (subsequently shown to be myxoid pseudotumor). Myxoid pseudotumor was identified by preoperative computed tomography imaging in 2 patients (6%) and identified by the gross dissector in 9 cases (27%). The mean size was 14 mm (range: 5 to 38 mm). All cases had an admixture of adipocytes, myxoid stromal matrix, variable collagenization, and a hypocellular population of bland spindled and stellate stromal cells. No multilobated atypical stromal cells were present. Clinical follow-up was available for 28 patients (90%), ranging from 1 to 132 months (mean: 24.6 mo). No patients had adverse events related to the myxoid pseudotumor. Myxoid pseudotumor of the renal sinus is often associated with a variety of adjacent neoplastic and non-neoplastic conditions and may present as a mass lesion detectable by imaging and/or gross inspection. Awareness of this benign process is important to avoid confusion with a neoplasm, especially liposarcoma.

Primary cutaneous extraskeletal osteosarcoma: a series of 16 cases.

Extraskeletal osteosarcoma (EOS) is a high grade soft tissue tumour characterised by the production of malignant osteoid, without attachment/involvement of underlying bone/periosteum. Rarely, EOS presents as a cutaneous tumour. The clinical behaviour of primary cutaneous EOS (PC-EOS) remains incompletely characterised. Herein we present the largest case series of PC-EOS reported to date. Sixteen PC-EOS cases from the archives/consultation files were retrieved (male:female 1:1; age 31-96 years, mean age 66 years). The tumours measured 1-10 cm (mean 3.2 cm) and were located on the lower extremity (7), head (6), upper extremity (2), and trunk (1). They consisted of pleomorphic, spindled-to-epithelioid cells, with fascicular, nodular, or sheet-like growth patterns and foci of malignant osteoid. Immunohistochemistry did not reveal specific lines of differentiation, and there was no evidence of other tumour types. A literature review was conducted to identify all well characterised cases of PC-EOS. A combined analysis of present and past cases was performed to determine overall trends in clinical characteristics and outcomes. The mean follow-up period was 23.9 months, during which 67.5% of patients experienced progression-free survival and 18% of patients died of disease. Rates of local recurrence and metastasis were 10% and 25%, respectively, approximately double past estimates. These data suggest that the prognosis of PC-EOS is less favourable than previously thought. The differential diagnosis includes benign entities (e.g., ossifying pyogenic granuloma) and malignant neoplasms with heterologous osteosarcomatous differentiation (e.g., carcinosarcoma, transdifferentiated melanoma). Wide excision remains the standard of care, and the role of chemotherapy and radiation remains inconclusive. Recognition of this rare entity can facilitate prompt diagnosis and appropriate treatment.

The capillary lobule variant of radiation-associated angiosarcoma in the setting of breast cancer: A diagnostic pitfall.

AIM: Post-radiation angiosarcoma is an iatrogenic event seen in the setting of breast cancer treatment. Histopathologically, there are morphologic variants of angiosarcoma that mimic benign entities, including the capillary lobule variant of post-radiation angiosarcoma. We present the largest case series to date of this histopathologic variant of post-radiation angiosarcoma. METHODS AND RESULTS: Cases of the capillary lobule variant of post-radiation angiosarcoma from institutional/consultation archives from 2008 to June 2022 were reviewed. For inclusion, tumors had to occur in irradiated skin and exhibit a multi-lobular proliferation of tightly packed capillary-like vessels, as previously described in this variant. Prior ancillary studies were also reviewed. Eight cases met the criteria. All occurred in women treated with radiation for breast cancer (median age 75 years). All cases had similar findings, including a multi-lobular proliferation of tightly packed vessels, infiltrative cords, and atypical single endothelial cells. A conventional angiosarcoma pattern was also seen in five cases. All cases tested were positive for vascular markers (CD31, CD34, and/or ERG) and MYC. MYC amplification was shown by FISH in all cases tested. Smooth muscle actin (SMA) was positive in pericytes in the capillary lobules in all five cases tested and areas of conventional angiosarcoma in two of three cases. CONCLUSIONS: The capillary lobule variant of angiosarcoma is a rare and therefore potentially under-recognized variant of post-radiation angiosarcoma. The lobular architecture and SMA positivity may mimic benign vascular proliferations. Careful attention to histopathologic features and ancillary tests may facilitate accurate diagnosis.