Melanoma arising in extracutaneous cellular blue naevus: report of two cases with comparison to cutaneous counterparts and uveal melanoma.

AIMS: Blue naevi are benign melanocytic lesions that typically occur in the dermis. Melanoma arising in blue naevus is rare, and shows a molecular profile distinct from conventional forms of cutaneous melanoma and more similar to uveal melanoma and central nervous system (CNS) melanocytomas. In contrast to conventional cutaneous melanoma, these tumour types typically show activating driver mutations in GNAQ or GNA11, a low mutational burden without evidence of a UV signature and a reproducible pattern of chromosomal copy number changes. Blue naevi can also occur at extracutaneous sites. Here we report two cases of melanoma arising in extracutaneous blue naevus and compare their molecular features to cohorts of melanoma arising in cutaneous blue naevus (five patients) and uveal melanoma (six patients). METHODS AND RESULTS: We describe the clinical, histomorphological, immunohistochemical and molecular findings in these two cases of melanoma arising in extracutaneous blue naevus. We compare their molecular profiles to melanomas arising in cutaneous blue naevus and uveal melanoma using a targeted next-generation DNA sequencing platform and find striking similarities between all three groups. CONCLUSIONS: The close relationship between blue naevus-associated melanomas, regardless of their anatomical site, supports and validates the concept of melanoma arising in extracutaneous blue naevus and suggests that the two groups share common pathogenic mechanisms. The similarity of both groups to uveal melanoma in turn supports the close relationship between blue naevus-associated melanoma, uveal melanoma and CNS melanocytoma, and their distinction from conventional UV-associated melanoma. These findings have important implications for prognosis and therapy.

Updates from the 2020 World Health Organization Classification of Soft Tissue and Bone Tumours.

The fifth edition of the World Health Organization (WHO) classification of soft tissue and bone tumours was published in May 2020. This 'Blue Book', which is also available digitally for the first time, incorporates an array of new information on these tumours, amassed in the 7 years since the previous edition. Major advances in molecular characterisation have driven further refinements in classification and the development of ancillary diagnostic tests, and have improved our understanding of disease pathogenesis. Several new entities are also included. This review summarises the main changes introduced in the 2020 WHO classification for each subcategory of soft tissue and bone tumours.

Primary intra-abdominal melanoma arising in association with extracutaneous blue naevus: a report of two cases.

AIMS: Blue naevi are uncommon dermal melanocytic neoplasms characterised by GNAQ/GNA11 mutations, which very rarely progress to melanoma. Such melanomas also often have BAP1 mutations, and lack genetic events associated with conventional melanoma. Exceptionally, blue naevi arise in extracutaneous locations; one melanoma arising in this setting has been reported. We report the clinicopathological, immunohistochemical and molecular genetic features of two cases of melanoma arising in extracutaneous blue naevus. METHODS AND RESULTS: Both arose in males, aged 25 and 63 years, with no history of other melanocytic lesions, and presented as large, painful intra-abdominal masses. The tumours were dark-brown/black, multilobulated, involved small intestinal mesentery and consisted of a predominantly fascicular and spindled, but occasionally nested and epithelioid, proliferation of variably pigmented, relatively monotonous cells with pale cytoplasm and ovoid nuclei with mild to moderate atypia. Mitotic activity was variable but generally low. Both cases showed areas of conventional and cellular blue naevus. Recurrent tumour in one case showed predominantly epithelioid morphology and greater cytological atypia and mitotic activity. One case expressed Melan-A, SOX10 and CD117, with absent expression of S100 protein and DOG1; the other expressed Melan-A, HMB45 and S100 protein. Next-generation sequencing identified GNAQ and BAP1 mutations in one case and GNA11 mutation in the other. Both patients developed widespread metastatic disease. CONCLUSION: Exceptionally rare, aggressive melanomas arising in extracutaneous blue naevi should be distinguished from metastatic melanoma, gastrointestinal stromal tumour and malignant melanotic nerve sheath tumour, especially given the significant therapeutic and prognostic differences between these different entities.

Radiation-associated sarcomas other than malignant peripheral nerve sheath tumours demonstrate loss of histone H3K27 trimethylation†.

BACKGROUND AND AIMS: Complete loss of histone H3 lysine 27 trimethylation (H3K27me3) has recently emerged as a biomarker for malignant peripheral nerve sheath tumours (MPNST). Loss of H3K27me3 staining has also been reported in post-radiation MPNST; however, it has not been evaluated in a large series of radiation-associated sarcomas of different histological subtypes. The aim of this study was to assess H3K27me3 labelling by immunohistochemistry in radiation-associated sarcomas and to determine the prevalence of H3K27me3 loss in these tumours. METHODS AND RESULTS: Radiation-associated sarcomas (n = 119) from two tertiary care referral centres were evaluated for loss of H3K27me3, defined as complete loss of staining within tumour cells in the presence of a positive internal control. Twenty-three cases (19%) showed H3K27me3 loss, including nine of 10 (90%) MPNST, seven of 77 (9%) undifferentiated spindle cell/pleomorphic sarcomas, five of 25 (20%) angiosarcomas, one of five (20%) leiomyosarcomas and one of two (50%) osteosarcomas. CONCLUSIONS: Complete H3K27me3 loss was present in 19% of radiation-associated sarcomas in our series. Our findings demonstrate that loss of H3K27me3 is not specific for radiation-associated MPNST and may also occur in other histological subtypes of RAS, including radiation-associated undifferentiated spindle cell/pleomorphic sarcoma, angiosarcoma, leiomyosarcoma and osteosarcoma.

Sclerosing epithelioid mesenchymal neoplasm of the pancreas - a proposed new entity.

We have encountered pancreatic tumors with unique histologic features, which do not conform to any of the known tumors of the pancreas or other anatomical sites. We aimed to define their clinicopathologic features and whether they are characterized by recurrent molecular signatures. Eight cases were identified; studied histologically and by immunohistochemistry. Selected cases were also subjected to whole-exome sequencing (WES; n = 4), RNA-sequencing (n = 6), Archer FusionPlex assay (n = 5), methylation profiling using the Illumina MethylationEPIC (850k) array platform (n = 6), and TERT promoter sequencing (n = 5). Six neoplasms occurred in females. The mean age was 43 years (range: 26-75). Five occurred in the head/neck of the pancreas. All patients were treated surgically; none received neoadjuvant/adjuvant therapy. All patients are free of disease after 53 months of median follow-up (range: 8-94). The tumors were well-circumscribed, and the median size was 1.8 cm (range: 1.3-5.8). Microscopically, the unencapsulated tumors had a geographic pattern of epithelioid cell nests alternating with spindle cell fascicles. Some areas showed dense fibrosis, in which enmeshed tumor cells imparted a slit-like pattern. The predominant epithelioid cells had scant cytoplasm and round-oval nuclei with open chromatin. The spindle cells displayed irregular, hyperchromatic nuclei. Mitoses were rare. No lymph node metastases were identified. All tumors were positive for vimentin, CD99 and cytokeratin (patchy), while negative for markers of solid pseudopapillary neoplasm, neuroendocrine, acinar, myogenic/rhabdoid, vascular, melanocytic, or lymphoid differentiation, gastrointestinal stromal tumor as well as MUC4. Whole-exome sequencing revealed no recurrent somatic mutations or amplifications/homozygous deletions in any known oncogenes or tumor suppressor genes. RNA-sequencing and the Archer FusionPlex assay did not detect any recurrent likely pathogenic gene fusions. Single sample gene set enrichment analysis revealed that these tumors display a likely mesenchymal transcriptomic program. Unsupervised analysis (t-SNE) of their methylation profiles against a set of different mesenchymal neoplasms demonstrated a distinct methylation pattern. Here, we describe pancreatic neoplasms with unique morphologic/immunophenotypic features and a distinct methylation pattern, along with a lack of abnormalities in any of key genetic drivers, supporting that these neoplasms represent a novel entity with an indolent clinical course. Given their mesenchymal transcriptomic features, we propose the designation of "sclerosing epithelioid mesenchymal neoplasm" of the pancreas.

Smooth muscle tumors of the gastrointestinal tract: an analysis of prognostic features in 407 cases.

Smooth muscle tumors represent the second most common mural mesenchymal neoplasm in the gastrointestinal tract, but established criteria for prognostic assessment of these tumors are lacking. A large cohort of surgically resected intramural gastrointestinal smooth muscle tumors from 31 institutions was analyzed to identify potential prognostic features. Pathologic features were assessed by expert gastrointestinal and/or soft tissue pathologists at each center. Immunohistochemical confirmation was required. A total of 407 cases from the esophagus (n = 97, 24%), stomach (n = 180, 44%), small bowel (n = 74, 18%), and colorectum (n = 56, 14%) were identified. Patients ranged in age from 19 to 92 years (mean 55 years), with a slight female predominance (57%). Mean tumor size was 5.4 cm, with the largest tumor measuring 29 cm. Disease progression following surgery, defined as local recurrence, metastasis, or disease-related death, occurred in 56 patients (14%). Colorectal tumors were most likely to progress, followed by small bowel and gastric tumors. None of the esophageal tumors in this series progressed. Receiver operator characteristic analysis identified optimal cutoffs of 9.8 cm and 3 mitoses/5 mm2 for discriminating between progressive and non-progressive tumors. Histologic features strongly associated with progression by univariate analysis included moderate-to-severe atypia, high cellularity, abnormal differentiation (defined as differentiation not closely resembling that of normal smooth muscle), tumor necrosis, mucosal ulceration, lamina propria involvement, and serosal involvement (P < 0.0001 for all features). Age, sex, and margin status were not significantly associated with progression (P = 0.23, 0.82, and 0.07, respectively). A risk assessment table was created based on tumor site, size, and mitotic count, and Kaplan-Meier plots of progression-free survival for each subgroup revealed progression-based tiers. Based on our findings, it appears that nonesophageal gastrointestinal smooth muscle tumors measuring >10 cm and/or showing ≥3 mitoses/5 mm2 may behave aggressively, and therefore close clinical follow-up is recommended in these cases.

MYC expression has limited utility in the distinction of undifferentiated radiation-associated sarcomas from sporadic sarcomas and sarcomatoid carcinoma.

AIMS: MYC is a proto-oncogene that is frequently dysregulated in various malignancies, through translocation or amplification. Radiation-associated angiosarcoma frequently shows MYC amplification, and immunohistochemical expression has been shown to be a reliable surrogate marker for amplification, but less is known about MYC expression in other sarcoma types, despite reports of MYC amplification in some undifferentiated/unclassified radiation-associated sarcomas (RASs). Distinguishing putative RAS from non-radiation-associated sarcoma or sarcomatoid carcinoma can be difficult. The aim of this study was to determine the prevalence and potential diagnostic utility of MYC in this context, by evaluating MYC expression in a cohort of RASs, non-radiation-associated sarcomas, and sarcomatoid carcinomas. METHODS AND RESULTS: Three hundred and eighty-five neoplasms were evaluated, including 81 RASs (18 angiosarcomas; 57 undifferentiated sarcomas; three leiomyosarcomas; and three malignant peripheral nerve sheath tumours), 267 non-radiation-associated sarcomas, and 37 sarcomatoid carcinomas. Immunohistochemistry was performed with a monoclonal anti-MYC antibody. Staining in tumour cells was scored on the basis of extent (focal, 1-4%; multifocal, 5-49%; and diffuse, ≥50%) and intensity (strong, moderate, and weak). One hundred percent of radiation-associated angiosarcomas expressed MYC diffusely. Expression was infrequent among other types of RAS (9.5%), and the frequency was similar to that in non-radiation-associated sarcomas (9.7%). MYC expression was more common in sarcomatoid carcinomas, occurring in 43%. The extent and intensity of staining were variable in all groups. CONCLUSION: MYC expression is infrequent among RASs other than angiosarcoma, and has a similar prevalence in sporadic sarcomas. Given the frequency of expression in sarcomatoid carcinomas, MYC expression outside the context of radiation-associated angiosarcoma is of limited diagnostic utility, and should be interpreted with caution after exclusion of sarcomatoid carcinoma where relevant.

Novel Methylated DNA Markers Discriminate Advanced Neoplasia in Pancreatic Cysts: Marker Discovery, Tissue Validation, and Cyst Fluid Testing.

OBJECTIVES: Pancreatic cystic lesions (PCLs) may be precancerous. Those likely to harbor high-grade dysplasia (HGD) or pancreatic cancer (PC) are targets for surgical resection. Current algorithms to predict advanced neoplasia (HGD/PC) in PCLs lack diagnostic accuracy. In pancreatic tissue and cyst fluid (CF) from PCLs, we sought to identify and validate novel methylated DNA markers (MDMs) that discriminate HGD/PC from low-grade dysplasia (LGD) or no dysplasia (ND). METHODS: From an unbiased whole-methylome discovery approach using predefined selection criteria followed by multistep validation on case (HGD or PC) and control (ND or LGD) tissues, we identified discriminant MDMs. Top candidate MDMs were then assayed by quantitative methylation-specific polymerase chain reaction on archival CF from surgically resected PCLs. RESULTS: Of 25 discriminant MDMs identified in tissue, 13 were selected for validation in 134 CF samples (21 cases [8 HGD, 13 PC], 113 controls [45 ND, 68 LGD]). A tree-based algorithm using 2 CF-MDMs (TBX15, BMP3) achieved sensitivity and specificity above 90%. Discrimination was significantly better by this CF-MDM panel than by mutant KRAS or carcinoembryonic antigen, with areas under the receiver operating characteristic curve of 0.93 (95% confidence interval: 0.86-0.99), 0.71 (0.57-0.85), and 0.72 (0.60-0.84), respectively. Cutoffs for the MDM panel applied to an independent CF validation set (31 cases, 56 controls) yielded similarly high discrimination, areas under the receiver operating characteristic curve = 0.86 (95% confidence interval: 0.77-0.94, P = 0.2). DISCUSSION: Novel MDMs discovered and validated in tissue accurately identify PCLs harboring HGD/PC. A panel of 2 MDMs assayed in CF yielded results with potential to enhance current risk prediction algorithms. Prospective studies are indicated to optimize and further evaluate CF-MDMs for clinical use.

Characteristics of mismatch repair deficiency in sarcomas.

Due to the efficacy of immune checkpoint inhibitor therapy in tumors with deficient mismatch repair, there has been a surge in demand for mismatch repair deficiency testing in various tumor types. Mismatch repair deficiency is not known to play a significant role in the pathogenesis of sarcomas, and the utility of testing these tumor types is not established. This study aimed to determine the frequency, pattern, and clinicopathologic correlates of mismatch repair deficiency in sarcomas. Three hundred and four sarcomas were profiled using a genomic platform that employs massively parallel sequencing to interrogate 447 cancer-associated genes. Mismatch repair status was evaluated by determining the number of small insertion/deletion events occurring in homopolymer regions per megabase of exonic sequence data across all genes.  Molecular characteristics of mismatch repair-deficient sarcomas were compared to mismatch repair-deficient carcinomas (n = 70) also identified using the sequencing panel. Seven sarcomas (2.3%) were classified as mismatch repair-deficient: four unclassified sarcomas, and one each of pleomorphic rhabdomyosarcoma, epithelioid leiomyosarcoma and malignant PEComa. One patient had an established diagnosis of Lynch syndrome. In the remaining patients, the mismatch repair gene mutation was confirmed or suspected to be somatic. Mismatch repair immunohistochemistry confirmed the mismatch repair-deficiency status of all cases with alterations in the tested proteins. As expected, mismatch repair-deficient sarcomas showed a significantly elevated tumor mutation burden relative to mismatch repair-proficient sarcomas (median 16 versus 4.6, p < 0.001). However, in comparison to mismatch repair-deficient carcinomas, mismatch repair-deficient sarcomas showed a lower tumor mutation burden (median 28 versus 16, p = 0.006) and a significantly greater degree of chromosomal instability. Among mismatch repair-deficient sarcomas, PD-L1 was variably expressed on tumor-associated macrophages but not on tumor cells. Three patients received pembrolizumab: two progressed and one has stable disease with five months follow-up. Mismatch repair deficiency in histologically classifiable sarcomas is rare (1%) and is more common in unclassified sarcomas (10%). Additional study is required to determine the predictive role of mismatch repair-deficiency in sarcomas for immunotherapy.

Germline cancer susceptibility gene variants, somatic second hits, and survival outcomes in patients with resected pancreatic cancer.

PURPOSE: Germline variants in double-strand DNA damage repair (dsDDR) genes (e.g., BRCA1/2) predispose to pancreatic adenocarcinoma (PDAC) and may predict sensitivity to platinum-based chemotherapy and poly(ADP) ribose polymerase (PARP) inhibitors. We sought to determine the prevalence and significance of germline cancer susceptibility gene variants in PDAC with paired somatic and survival analyses. METHODS: Using a customized next-generation sequencing panel, germline/somatic DNA was analyzed from 289 patients with resected PDAC ascertained without preselection for high-risk features (e.g., young age, personal/family history). All identified variants were assessed for pathogenicity. Outcomes were analyzed using multivariable-adjusted Cox proportional hazards regression. RESULTS: We found that 28/289 (9.7%; 95% confidence interval [CI] 6.5-13.7%) patients carried pathogenic/likely pathogenic germline variants, including 21 (7.3%) dsDDR gene variants (3 BRCA1, 4 BRCA2, 14 other dsDDR genes [ATM, BRIP1, CHEK2, NBN, PALB2, RAD50, RAD51C]), 3 Lynch syndrome, and 4 other genes (APC p.I1307K, CDKN2A, TP53). Somatic sequencing and immunohistochemistry identified second hits in the tumor in 12/27 (44.4%) patients with germline variants (1 failed sequencing). Compared with noncarriers, patients with germline dsDDR gene variants had superior overall survival (hazard ratio [HR] 0.54; 95% CI 0.30-0.99; P = 0.05). CONCLUSION: Nearly 10% of PDAC patients harbor germline variants, although the majority lack somatic second hits, the therapeutic significance of which warrants further study.

Loss of SMAD4 protein expression in gastrointestinal and extra-gastrointestinal carcinomas.

AIMS: SMAD4 (DPC4) is a tumour suppressor gene that is dysregulated in various tumour types, particularly pancreaticobiliary and gastrointestinal carcinomas. Corresponding loss of protein expression has been reported in approximately 50% of pancreatic and 25% of colonic adenocarcinomas. In the evaluation of carcinoma of unknown primary site, immunohistochemical loss of SMAD4 expression is often used to suggest pancreaticobiliary origin, but there are limited data on the spectrum of SMAD4 expression in carcinomas of other sites. This study evaluates the frequency of SMAD4 loss in a large cohort of carcinomas from diverse anatomical sites. METHODS AND RESULTS: Immunohistochemistry for SMAD4 was performed on tissue microarrays or whole tissue sections of 1210 carcinomas from various organs: gastrointestinal tract, liver, pancreas/biliary tract, lung, breast, thyroid, kidney, ovary and uterus. Expression was considered lost when there was complete absence of staining in tumour cell nuclei, in the presence of intact staining in non-neoplastic cells. SMAD4 loss was seen in 58% of pancreatic adenocarcinomas, 27% of appendiceal adenocarcinomas, 19% of colorectal adenocarcinomas, 16% of cholangiocarcinomas, 10% of lung adenocarcinomas and <5% of oesophageal, breast, gastric and mucinous ovarian adenocarcinomas. All papillary thyroid, hepatocellular, non-mucinous ovarian, endometrial and renal cell carcinomas showed intact SMAD4 nuclear expression. CONCLUSION: In addition to pancreaticobiliary, appendiceal and colonic tumours, SMAD4 loss is also seen in a small subset of other carcinomas, specifically breast, lung, oesophageal and gastric adenocarcinomas, all of which are typically CK7-positive, similar to pancreaticobiliary carcinoma. Awareness of SMAD4 loss in these other carcinoma types is helpful in the evaluation of carcinomas of unknown or uncertain primary site.

Atypical lipomatous tumour/well-differentiated liposarcoma and de-differentiated liposarcoma in patients aged ≤ 40 years: a study of 116 patients.

AIMS: Limited data exist on atypical lipomatous tumour (ALT)/well-differentiated liposarcoma (WDL) and de-differentiated liposarcoma (DDLPS) in children and young adults. METHODS AND RESULTS: Cases of ALT/WDL/DDLPS arising in patients aged ≤ 40 years were collected from multiple institutional and consultation archives. A total of 116 cases of ALT/WDL (75) and DDLPS (41) were identified, representing fewer than 5% of these tumours seen at our institutions during this time-period. The patients (59 male/57 female) ranged in age from 8 to 40 years. Sites included deep central (abdomen/retroperitoneum/pelvis/groin) (n = 60), extremity (n = 42), trunk (n = 5), head/neck (n = 8) and mediastinum (n = 1). De-differentiated patterns included: high-grade pleomorphic sarcoma, myxofibrosarcoma-like, heterologous rhabdomyoblastic differentiation, low-grade spindle cell sarcoma and homologous lipoblastic differentiation. Forty-one patients experienced a local recurrence and 11 patients with DDLPS developed metastasis. ALT arising in the extremities had lower recurrence rates than deep central WDL (5-year recurrence-free survival 88.9% versus 59.0%; P = 0.002), while patients with deep central DDLPS experienced significantly more adverse events compared to WDL at this site (5-year event-free survival 11.9% versus 59.0%) (P < 0.0001). Seven (of eight) head/neck tumours had follow-up available; five recurred, and one patient (DDLPS) with recurrence also experienced a metastasis. The single mediastinal tumour (DDLPS) recurred and metastasised. CONCLUSION: ALT/WDL and DDLPS occurring in patients aged ≤ 40 years is rare, but exhibits similar morphological features to its counterparts in older adults, including potential for heterologous and homologous de-differentiation in the latter. Although case numbers are limited, tumours arising in the head and neck exhibit high rates of adverse events, suggesting that classification as WDL rather than ALT is more appropriate.

Primordial germ cells as a potential shared cell of origin for mucinous cystic neoplasms of the pancreas and mucinous ovarian tumors.

Mucinous ovarian tumors (MOTs) morphologically and epidemiologically resemble mucinous cystic neoplasms (MCNs) of the pancreas, sharing a similar stroma and both occurring disproportionately among young females. Additionally, MOTs and MCNs share similar clinical characteristics and immunohistochemical phenotypes. Exome sequencing has revealed frequent recurrent mutations in KRAS and RNF43 in both MOTs and MCNs. The cell of origin for these tumors remains unclear, but MOTs sometimes arise in the context of mature cystic teratomas and other primordial germ cell (PGC) tumors. We undertook the present study to investigate whether non-teratoma-associated MOTs and MCNs share a common cell of origin. Comparisons of the gene expression profiles of MOTs [including both the mucinous borderline ovarian tumors (MBOTs) and invasive mucinous ovarian carcinomas (MOCs)], high-grade serous ovarian carcinomas, ovarian surface epithelium, Fallopian tube epithelium, normal pancreatic tissue, pancreatic duct adenocarcinomas, MCNs, and single-cell RNA-sequencing of PGCs revealed that both MOTs and MCNs are more closely related to PGCs than to either eutopic epithelial tumors or normal epithelia. We hypothesize that MCNs may arise from PGCs that stopped in the dorsal pancreas during their descent to the gonads during early human embryogenesis, while MOTs arise from PGCs in the ovary. Together, these data suggest a common pathway for the development of MCNs and MOTs, and suggest that these tumors may be more properly classified as germ cell tumor variants. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Lymph node metastases in resected pancreatic ductal adenocarcinoma: predictors of disease recurrence and survival.

BACKGROUND: Few studies have simultaneously assessed the prognostic value of the multiple classification systems for lymph node (LN) metastases in resected pancreatic ductal adenocarcinoma (PDAC). METHODS: In 600 patients with resected PDAC, we examined the association of LN parameters (AJCC 7th and 8th editions, LN ratio (LNR), and log odds of metastatic LN (LODDS)) with pattern of recurrence and patient survival using logistic regression and Cox proportional hazards regression, respectively. Regression models adjusted for age, sex, margin status, tumour grade, and perioperative therapy. RESULTS: Lymph node metastases classified by AJCC 7th and 8th editions, LNR, and LODDS were associated with worse disease free-survival (DFS) and overall survival (OS) (all Ptrend<0.01). American Joint Committee on Cancer 8th edition effectively predicted DFS and OS, while minimising model complexity. Lymph node metastases had weaker prognostic value in patients with positive margins and distal resections (both Pinteraction<0.03). Lymph node metastases by AJCC 7th and 8th editions did not predict the likelihood of local disease as the first site of recurrence. CONCLUSIONS: American Joint Committee on Cancer 8th edition LN classification is an effective and practical tool to predict outcomes in patients with resected PDAC. However, the prognostic value of LN metastases is attenuated in patients with positive resection margins and distal pancreatectomies.

Advances in the clinicopathological and molecular classification of cutaneous mesenchymal neoplasms.

In recent years, there have been several important refinements in the classification of cutaneous mesenchymal neoplasms, including the description of new tumour types, along with the identification of novel and recurrent molecular genetic findings. In addition to providing new insights into tumour biology, many of these advances have had significant clinical consequences with regard to diagnostics, management, and prognostication. Newly described entities include pseudomyogenic haemangioendothelioma, haemosiderotic fibrolipomatous tumour, and fibroblastic connective tissue naevus, which are reviewed in the context of the principal differential diagnoses and significant clinical implications. Genetic characterization of several soft tissue tumour types that occur in the skin has resulted in the identification of diagnostically useful markers: ALK gene rearrangement with corresponding ALK protein expression by immunohistochemistry in epithelioid fibrous histiocytoma; the WWTR1-CAMTA1 fusion gene with CAMTA1 protein expression in epithelioid haemangioendothelioma; MYC amplification and overexpression in radiation-associated angiosarcoma; and EWSR1 gene rearrangement in cutaneous myoepithelial tumours. Finally, the classification of intradermal smooth muscle tumours and unclassified/pleomorphic dermal sarcoma has been refined, resulting in both improved classification and improved prognostication. Many of the tumour types listed above are encountered not only by specialist dermatopathologists, but also by practising general surgical pathologists, and this review should therefore provide a widely applicable update on the histological and molecular classification of cutaneous mesenchymal neoplasms, along with the appropriate use of ancillary diagnostic tests, in particular immunohistochemistry, in the evaluation of such lesions and their histological mimics.

Cytokeratin 17 is highly sensitive in discriminating cutaneous lymphadenoma (a distinct trichoblastoma variant) from basal cell carcinoma.

BACKGROUND: Cutaneous lymphadenoma (CL) is rare neoplasm that clinically and histologically resembles basal cell carcinoma (BCC). CL, composed of dermal basaloid epithelial islands with prominent admixed lymphocytes, characteristically contains cytokeratin 20 (CK20)-positive Merkel cells (MCs). However, CK20 may be of limited use because of low MC density in small samples. CK17 is expressed diffusely throughout BCC. We investigated the discriminatory utility of CK17 and CK20 in CL and BCC. METHODS: A retrospective clinicopathological review of 11 cases of CL and 14 BCC was performed. CK20-positive MCs within basaloid tumor lobules and CK17 immunohistochemical staining and pattern of expression were recorded. RESULTS: Intratumoral CK20-positive MCs were identified in 4/11 CL cases (36.4%) and 0/14 BCC cases (p = 0.012, sensitivity = 0.36). CK17 showed diffuse positive staining in all 14 BCC cases. CK17 showed a distinct patchy and peripheral rim staining in basaloid islands of 10/11 CL cases (p < 0.001, sensitivity = 0.91); one case showed patchy staining throughout tumor lobules. CONCLUSIONS: In cases with a differential diagnosis of CL and BCC, CK20 staining of intratumoral MCs has a high positive predictive value for CL but is of low sensitivity. The pattern of CK17 expression is a highly sensitive marker for distinguishing CL from BCC in small samples.

Gene fusion detection in formalin-fixed paraffin-embedded benign fibrous histiocytomas using fluorescence in situ hybridization and RNA sequencing.

Benign fibrous histiocytomas (FH) can be subdivided into several morphological and clinical subgroups. Recently, gene fusions involving either one of two protein kinase C genes (PRKCB and PRKCD) or the ALK gene were described in FH. We here wanted to evaluate the frequency of PRKCB and PRKCD gene fusions in FH. Using interphase fluorescence in situ hybridization on sections from formalin-fixed paraffin-embedded (FFPE) tumors, 36 cases could be analyzed. PRKCB or PRKCD rearrangements were seen in five tumors: 1/7 regular, 0/3 aneurysmal, 0/6 cellular, 2/7 epithelioid, 0/1 atypical, 2/10 deep, and 0/2 metastatic lesions. We also evaluated the status of the ALK gene in selected cases, finding rearrangements in 3/7 epithelioid and 0/1 atypical lesions. To assess the gene fusion status of FH further, deep sequencing of RNA (RNA-Seq) was performed on FFPE tissue from eight cases with unknown gene fusion status, as well as on two FH and six soft tissue sarcomas with known gene fusions; of the latter eight positive controls, the expected fusion transcript was found in all but one, while 2/8 FH with unknown genetic status showed fusion transcripts, including a novel KIRREL/PRKCA chimera. Thus, also a third member of the PRKC family is involved in FH tumorigenesis. We conclude that gene fusions involving PRKC genes occur in several morphological (regular, cellular, aneurysmal, epithelioid) and clinical (cutaneous, deep) subsets of FH, but they seem to account for only a minority of the cases. In epithelioid lesions, however, rearrangements of PRKC or ALK were seen, as mutually exclusive events, in the majority (5/7) of cases. Finally, the study also shows that RNA-Seq is a promising tool for identifying gene fusions in FFPE tissues.

ALK rearrangement and overexpression in epithelioid fibrous histiocytoma.

Epithelioid benign fibrous histiocytoma, also known as 'epithelioid cell histiocytoma,' has traditionally been considered a morphologic variant of cutaneous fibrous histiocytoma (dermatofibroma). In addition to its characteristic epithelioid cytomorphology, several phenotypic differences suggest that epithelioid fibrous histiocytoma may differ biologically from other variants. Recently, ALK rearrangement was described in two cases of epithelioid fibrous histiocytoma and separately in two cases reported as 'atypical' fibrous histiocytoma (with epithelioid features), with corresponding ALK expression detectable by immunohistochemistry. The goals of this study were to determine the frequency of ALK expression by immunohistochemistry in epithelioid fibrous histiocytoma, to determine its value for the diagnosis of epithelioid fibrous histiocytoma among variants and other histologic mimics, and to evaluate ALK gene rearrangement in epithelioid fibrous histiocytoma. ALK protein expression was evaluated in whole tissue sections from 33 epithelioid fibrous histiocytomas, 41 other cases of fibrous histiocytoma (11 conventional and 10 each cellular, atypical, and aneurysmal types), 10 cutaneous syncytial myoepitheliomas, and 5 atypical fibroxanthomas, using a mouse anti-ALK monoclonal antibody. Fluorescence in situ hybridization (FISH) was performed using break-apart probes. In total, 29/33 (88%) cases of epithelioid fibrous histiocytoma showed diffuse cytoplasmic ALK expression. Staining was moderate to strong in intensity in all cases except one, which showed diffuse weak expression. All other tumor types were negative for ALK expression. FISH demonstrated ALK rearrangement in all ALK-immunoreactive cases evaluated (n=13), and not in one ALK expression-negative epithelioid fibrous histiocytoma successfully examined. In conclusion, the majority of epithelioid fibrous histiocytomas demonstrate ALK expression and ALK gene rearrangement. ALK expression is not seen in other variants of fibrous histiocytoma, providing a useful diagnostic tool to distinguish epithelioid fibrous histiocytoma from most histologic mimics. The expression of ALK suggests that epithelioid fibrous histiocytoma is a biologically distinct tumor type, unrelated to conventional fibrous histiocytoma and histologic variants.

Microanatomy of the cervical and anorectal squamocolumnar junctions: a proposed model for anatomical differences in HPV-related cancer risk.

Human papilloma virus (HPV) infection causes cancers and their precursors (high-grade squamous intraepithelial lesions) near cervical and anal squamocolumnar junctions. Recently described cervical squamocolumnar junction cells are putative residual embryonic cells near the cervical transformation zone. These cells appear multipotential and share an identical immunophenotype (strongly CK7-positive) with over 90% of high-grade squamous intraepithelial lesions and cervical carcinomas. However, because the number of new cervical cancers discovered yearly world wide is 17-fold that of anal cancer, we posed the hypothesis that this difference in cancer risk reflects differences in the transition zones at the two sites. The microanatomy of the normal anal transformation zone (n=37) and topography and immunophenotype of anal squamous neoplasms (n=97) were studied. A discrete anal transition zone was composed of multilayered CK7-positive/p63-negative superficial columnar cells and an uninterrupted layer of CK7-negative/p63-positive basal cells. The CK7-negative/p63-positive basal cells were continuous with-and identical in appearance to-the basal cells of the mature squamous epithelium. This was in contrast to the cervical squamocolumnar junction, which harbored a single-layered CK7-positive/p63-negative squamocolumnar junction cell population. Of the 97 anal intraepithelial neoplasia/squamous cell carcinomas evaluated, only 27% (26/97) appeared to originate near the anal transition zone and only 23% (22/97) were CK7-positive. This study thus reveals two fundamental differences between the anus and the cervix: (1) the anal transition zone does not harbor a single monolayer of residual undifferentiated embryonic cells and (2) the dominant tumor immunophenotype is in keeping with an origin in metaplastic (CK7-negative) squamous rather than squamocolumnar junction (CK7-positive) epithelium. The implication is that, at birth, the embryonic cells in the anal transition zone have already begun to differentiate, presenting a metaplasia that-similar to vaginal and vulvar epithelium-is less prone to HPV-directed carcinogenesis. This in turn underscores the link between cancer risk and a very small and discrete population of vulnerable squamocolumnar junction cells in the cervix.