Primary Pulmonary Myxoid Sarcoma and Thoracic Angiomatoid Fibrous Histiocytoma: Two Sides of the Same Coin?

Primary pulmonary myxoid sarcoma (PPMS) and thoracic angiomatoid fibrous histiocytoma (AFH) are rare neoplasms with EWSR1 fusions and overlapping morphology. Both tumor types often show epithelial membrane antigen expression, but AFH characteristically co-expresses desmin. We encountered a case of PPMS with the unexpected finding of patchy, strong anaplastic lymphoma kinase (ALK) (previously reported in AFH) and synaptophysin expression. We evaluated a cohort of PPMS and thoracic AFH with systematic morphologic comparison and surveyed for aberrant expression of ALK and synaptophysin. Medical records and slides were reviewed for 16 molecularly confirmed cases of PPMS (n=5) and thoracic AFH (n=11). Each case was scored for morphologic characteristics typical of PPMS and/or AFH. ALK, synaptophysin, chromogranin, desmin, and epithelial membrane antigen immunostains were performed on cases with available tissue. AFH and PPMS cases showed similar age at presentation and long-term tumor behavior. Almost all cases of PPMS and AFH had a fibrous pseudocapsule and lymphoid rim. All PPMS had myxoid stroma and reticular growth pattern, but these features were also present in a subset of AFH. Synaptophysin expression was present in 6 of 11 AFH and 1 of 5 PPMS; all tested cases were negative for chromogranin (n=15). One case of AFH and 1 case of PPMS showed focally strong coexpression of synaptophysin and ALK. AFH and PPMS show considerable clinicopathologic overlap. When supportive, the immunohistochemical findings described may aid in diagnosis before molecular confirmation. PPMS and AFH may be morphologic variants of the same clinicopathologic entity, which can show more immunophenotypic variability than previously reported.

Imaging features of perinephric myxoid pseudotumors of fat

OBJECTIVE

Retrospectively evaluate multimodality imaging features of perinephric myxoid pseudotumor of fat (PMPTF).

METHODS

Institutional cases of PMPTF with CT, MRI and/or ultrasound evaluation from 1/1/2020 to 9/1/2023 were retrospectively reviewed. Patient demographics and clinical history were reviewed, and imaging features recorded.

RESULTS

14 patients with pathologically-proven PMPTF were identified (11 M, 3 F; mean age 66.7 ± 17.0 years; range 40-87 years). Three patients (18%) had bilateral lesions; a total of 17 PMPTFs were reviewed. 15/17 (88%) were biopsy-proven; two cases were diagnosed by imaging only in patients with a contralateral biopsy-proven PMPTF. All evaluable specimens were negative for MDM2 amplification. 11/17 (65%) occurred in patients with renal disease, including 4/17 (24%) in patients with renal transplant. 100% (17/17) had CT, 11/17 (65%) MRI, and 6/17 (35%) ultrasound. The mean largest lesion dimension was 10.9 ± 4.6 cm (range 4.3-17.0 cm). Of cases involving native kidneys, 7/13 (54%) presented as multifocal perinephric masses and 5/13 (38%) as a solitary perinephric mass. All four transplant cases presented as infiltrative-appearing masses involving the renal sinus with lesser perinephric involvement. 14/17 (82%) lesions contained macroscopic fat on CT and MRI and 3/17 (18%) showed no macroscopic fat, all involving renal transplants. All cases with MRI demonstrated T2 hyperintensity with signal dropout on opposed-phase imaging. 11/13 (85%) PMPTF showed no or equivocal CT enhancement. Enhancement was better seen on MRI in all cases evaluated by both CT and MRI. Of the six PMPTFs imaged by ultrasound, four (67%) were heterogeneously hypoechoic and two (33%) had mixed regions of hypo-, iso- and hyperechogenicity relative to adjacent renal parenchyma.

CONCLUSIONS

PMPTF is a rare, benign, and underrecognized lesion that may mimic malignancy, particularly retroperitoneal well-differentiated liposarcoma. The imaging features of this unusual pseudosarcoma differ in native and transplanted kidneys. Improved awareness of this entity will facilitate appropriate patient management and avoid unnecessary intervention.

Malignant glomus tumor arising in association with a fumarate hydratase-deficient leiomyoma: An unusual collision tumor

Collision tumors, defined as "two independent neoplasms that occur in close proximity to one another but maintain distinct boundaries," are quite rare. We report an exceptional collision tumor composed of a genetically confirmed malignant glomus tumor and a fumarate hydratase (FH)-deficient leiomyoma, presenting as a subcutaneous thigh mass in a 38-year-old male who was known to have hereditary leiomyomatosis and renal cell carcinoma syndrome. Microscopic examination identified a biphasic subcutaneous mass comprising sheets and nodules of glomus cells, with nuclear atypia and mitotic activity, and fascicles of mitotically inactive smooth muscle with variably pleomorphic nuclei and intracytoplasmic eosinophilic inclusions, features of FH-deficient leiomyoma. Immunohistochemistry demonstrated loss of FH and robust 2-succinocysteine expression in the smooth muscle, with a normal (FH-retained) expression pattern in the glomus tumor. Next-generation sequencing, performed on the glomus tumor component, identified CARMN::NOTCH2 fusion, characteristic of malignant glomus tumors. Awareness of the distinctive morphologic, immunohistochemical, and molecular genetic features of glomus tumors and FH-deficient leiomyomas is important for correct clinical management of patients with exceptional collision tumors of this type.

Pulmonary gangliocytic paraganglioma: An under-recognized mimic of carcinoid tumor

Gangliocytic paragangliomas are rare neoplasms occurring almost exclusively in the ampullary region of the gastrointestinal tract. Although these tumors are not typically considered in the differential diagnosis of primary pulmonary neoplasia, 5 cases of primary pulmonary gangliocytic paragangliomas have been previously reported. Herein we report our experience with 3 additional examples, all referred to our Anatomic Pathology Consultation service. The patients (a 32-year-old man, a 69-year-old woman and a 55-year-old man) each presented with an endobronchial (2 cases) or upper lobe lung mass, ranging from 1.5 to 2.5 cm in maximum dimension. Biopsy and endobronchial debulking specimens demonstrated the classic triphasic morphology of gangliocytic paraganglioma, with epithelial, spindled and ganglion-like cells. By immunohistochemistry, the tumors were positive for keratin, synaptophysin and chromogranin A in the epithelial component, S100 protein and glial fibrillary acidic protein (GFAP) in the Schwannian spindled cells, and synaptophysin in ganglion cells. TTF1 expression was seen in the epithelial components of 2 cases. The Ki-67 labelling index was low (<2%). Primary pulmonary gangliocytic paragangliomas should be distinguished from carcinoid tumors, given the different natural histories and risk stratification approaches for these morphologically similar tumors. Awareness that gangliocytic paraganglioma may occur in the lung and appropriate immunohistochemical studies are key to correct diagnosis.

Xanthogranulomatous Epithelial Tumors and Keratin-Positive Giant Cell Rich Tumors of Soft Tissue and Bone: Two Sides of the Same Coin

Xanthogranulomatous epithelial tumor is a recently described soft tissue tumor characterized by subcutaneous location, partial encapsulation, a xanthogranulomatous inflammatory cell infiltrate, and keratin-positive mononuclear cells. It shares some morphologic features with keratin-positive, giant cell-rich soft tissue tumors. Both have recently been shown to harbor HMGA2::NCOR2 fusions. The relationship between these tumors and their differential diagnosis with other osteoclast-containing soft tissue tumors is discussed.

Vascular tumors of intermediate malignancy: An update

The term "hemangioendothelioma" is used for endothelial neoplasms of intermediate malignancy and describes a group of rare neoplasms having biologic behavior falling in between that of the benign hemangiomas and fully malignant angiosarcomas. The hemangioendotheliomas fall into several specific, clinicopathologically and genetically distinct entities, specifically epithelioid hemangioendothelioma, kaposiform hemangioendothelioma, papillary intralymphatic angioendothelioma and retiform hemangioendothelioma (hobnailed hemangioendothelioma), pseudomyogenic hemangioendothelioma, composite hemangioendothelioma, and YAP1::TFE3-fused hemangioendothelioma. The clinical, morphologic, immunohistochemical, and genetic features, and the differential diagnosis of each of these rare entities are discussed in this review.

Sarcomas Harboring EWSR1::PATZ1 Fusions: A Clinicopathologic Study of 17 Cases

Soft tissue sarcomas harboring EWSR1::PATZ1 are a recently recognized entity with variable morphology and a heterogeneous immunohistochemical profile. We studied 17 such tumors. The tumors occurred in 12 men and 5 women (median age, 50 years; range, 15-71 years), involved the thoracoabdominal soft tissues (14 cases; 82%), lower extremities (2 cases; 12%), and tongue (1 case; 6%), and ranged from 0.7 to 11.3 cm (median, 4.7 cm). All but 1 patient received complete surgical resection; 7 were also treated with neoadjuvant chemo/radiotherapy. All cases showed typical features of EWSR1::PATZ1 sarcoma, including uniform round to spindled cells, fibromyxoid matrix, fibrous bands, hyalinized vessels, and pseudoalveolar/microcystic spaces. Unusual features, seen in a subset of cases, included degenerative-appearing nuclear atypia, epithelioid cytomorphology, mature fat, abundant rhabdomyoblasts, high mitotic activity, and foci with increased cellularity and nuclear atypia. Positive immunohistochemical results were desmin (16/17, 94%), MyoD1 (13/14, 93%), myogenin (6/14, 43%), GFAP (10/10, 100%), S100 protein (15/17, 88%), SOX10 (7/13, 54%), keratin (10/17, 59%), CD99 (4/11, 36%), H3K27me3 (retained expression 9/9, 100%), p16 (absent expression 1/4, 25%), and p53 (wild type 3/3, 100%). Fusion events included EWSR1 exon 8::PATZ1 exon 1 (14/17, 82%), EWSR1 exon 9::PATZ1 exon 1 (2/17, 12%), and EWSR1 exon 7::PATZ1 exon 1 (1/17, 6%). No evaluated tumor had alterations of CDKN2A/B and/or TP53, or MDM2 amplification. Clinical follow-up (16 patients: median, 13.5 months; range, 1-77 months) showed distant metastases in 3 patients (1/3 at time of presentation) and no local recurrences. At the time of last follow-up, 14 patients were disease free, 1 was alive with disease, 1 was dead of disease (at 13 months), and 1 had an indeterminant pulmonary nodule. We conclude that the morphologic spectrum of EWSR1::PATZ1 is broader than has been previously appreciated. Although more long-term follow-up is needed, the prognosis of these very rare sarcomas may be more favorable than previously reported.

CSF1 expression in xanthogranulomatous epithelial tumor/keratin-positive giant cell-rich tumor

"Xanthogranulomatous epithelial tumor" (XGET) and "keratin-positive giant cell-rich soft tissue tumor" (KPGCT), two recently described mesenchymal neoplasms, likely represent different aspects of a single entity. Both tumors are composed of only a small minority of tumor cells surrounded by large numbers of non-neoplastic inflammatory cells and histiocytes, suggesting production of a paracrine factor with resulting "landscape effect," as seen in tenosynovial giant cell tumor. Recent evidence suggests that the paracrine factor in XGET/KPGCT may be CSF1, as in tenosynovial giant cell tumor. We hypothesized that CSF1 is overexpressed in XGET/KPGCT. To test our hypothesis, we performed quantitative real time PCR (qPCR) for CSF1 expression and CSF1 RNAscope chromogenic in situ hybridization (CISH) on 6 cases of XGET/KPGCT. All cases were positive with CSF1 CISH and showed increased expression of CSF1 by qPCR. Our findings provide additional evidence that the CSF1/CSF1R pathway is involved in the pathogenesis of XGET/KPGCT. These findings suggest a possible role for CSF1R inhibition in the treatment of unresectable or metastatic XGET/KPGCT.

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.

EWSR1::POU2AF3(COLCA2) Sarcoma: An Aggressive, Polyphenotypic Sarcoma With a Head and Neck Predilection

EWSR1::POU2AF3 (COLCA2) sarcomas are a recently identified group of undifferentiated round/spindle cell neoplasms with a predilection for the head and neck region. Herein, we report our experience with 8 cases, occurring in 5 men and 3 women (age range, 37-74 years; median, 60 years). Tumors involved the head/neck (4 cases), and one each the thigh, thoracic wall, fibula, and lung. Seven patients received multimodal therapy; 1 patient was treated only with surgery. Clinical follow-up (8 patients; range, 4-122 months; median, 32 months) showed 5 patients with metastases (often multifocal, with a latency ranging from 7 to 119 months), and 3 of them also with local recurrence. The median local recurrence-free and metastasis-free survival rates were 24 months and 29 months, respectively. Of the 8 patients, 1 died of an unknown cause, 4 were alive with metastatic disease, 1 was alive with unresectable local disease, and 2 were without disease. The tumors were composed of 2 morphologic subgroups: (1) relatively bland tumors consisting of spindled to stellate cells with varying cellularity and fibromyxoid stroma (2 cases) and (2) overtly malignant tumors composed of nests of "neuroendocrine-appearing" round cells surrounded by spindled cells (6 cases). Individual cases in the second group showed glandular, osteogenic, or rhabdomyoblastic differentiation. Immunohistochemical results included CD56 (4/4 cases), GFAP (5/8), SATB2 (4/6), keratin (AE1/AE3) (5/8), and S100 protein (4/7). RNA sequencing identified EWSR1::POU2AF3 gene fusion in all cases. EWSR1 gene rearrangement was confirmed by fluorescence in situ hybridization in 5 cases. Our findings confirm the head/neck predilection and aggressive clinical behavior of EWSR1::POU2AF3 sarcomas and widen the morphologic spectrum of these rare lesions to include relatively bland spindle cell tumors and tumors with divergent differentiation.

Klotho Overexpression Is Frequently Associated With Upstream Rearrangements in Fusion-Negative Phosphaturic Mesenchymal Tumors of Bone and Sinonasal Tract

Phosphaturic mesenchymal tumors (PMT) are uncommon neoplasms that cause hypophosphatemia/osteomalacia mainly by secreting fibroblast growth factor 23. We previously identified FN1::FGFR1/FGF1 fusions in nearly half of the PMTs and frequent KL (Klotho or α-Klotho) overexpression in only those with no known fusion. Here, we studied a larger cohort of PMTs for KL expression and alterations. By FN1 break-apart fluorescence in situ hybridization (FISH) and reappraisal of previous RNA sequencing data, 6 tumors previously considered "fusion-negative" (defined by negative results of FISH for FN1::FGFR1 fusion and FGF1 break-apart and/or of RNA sequencing) were reclassified as fusion-positive PMTs, including 1 containing a novel FN1::ZACN fusion. The final cohort of fusion-negative PMTs included 33 tumors from 32 patients, which occurred in the bone (n = 18), soft tissue (n = 10), sinonasal tract (n = 4), and brain (n = 1). In combination with previous work, RNA sequencing, RNA in situ hybridization, and immunohistochemistry showed largely concordant results and demonstrated KL/α-Klotho overexpression in 17 of the 28 fusion-negative and none of the 10 fusion-positive PMTs studied. Prompted by a patient in this cohort harboring germline KL upstream translocation with systemic α-Klotho overexpression and multifocal PMTs, FISH was performed and revealed KL rearrangement in 16 of the 33 fusion-negative PMTs (one also with amplification), including 14 of the 17 cases with KL/α-Klotho overexpression and none of the 11 KL/α-Klotho-low fusion-negative and 11 fusion-positive cases studied. Whole genomic sequencing confirmed translocation and inversion in 2 FISH-positive cases involving the KL upstream region, warranting further investigation into the mechanism whereby these rearrangements may lead to KL upregulation. Methylated DNA immunoprecipitation and sequencing suggested no major role of promoter methylation in KL regulation in PMT. Interestingly, KL-high/-rearranged cases seemed to form a clinicopathologically homogeneous group, showing a predilection for skeletal/sinonasal locations and typically matrix-poor, cellular solitary fibrous tumor-like morphology. Importantly, FGFR1 signaling pathways were upregulated in fusion-negative PMTs regardless of the KL status compared with non-PMT mesenchymal tumors by gene set enrichment analysis, perhaps justifying FGFR1 inhibition in treating this subset of PMTs.

Pseudoendocrine sarcoma: clinicopathologic, molecular, and epigenetic features of one case

Pseudoendocrine sarcoma (PES) is a recently described neoplasm typically arising in paravertebral soft tissues. Histologically, PES resembles well-differentiated neuroendocrine tumors but lacks expression of epithelial/neuroendocrine markers, and most show aberrant nuclear β-catenin positivity. We describe the clinicopathological and molecular features and DNA methylation profile of one PES. A resected paraspinal soft tissue mass in a 52-year-old man showed a neuroendocrine-like neoplasm, negative for keratin, and synaptophysin and showing diffuse nuclear β-catenin expression. Targeted NGS confirmed a CTNNB1 (p.S37C) mutation. Whole genome methylation analysis showed no match to any methylation class in the central nervous system tumor (versions 11b6 and 12b6) or sarcoma classifier (calibrated scores of ≤0.3), but clustered together with a recently reported PES in which methylation analysis was also performed. He remained disease-free for 18 months after surgery, followed by chemoradiation. As more cases are examined, our findings suggest that PES may have a unique methylation profiling signature.

Fusion-driven Spindle Cell Rhabdomyosarcomas of Bone and Soft Tissue: A Clinicopathologic and Molecular Genetic Study of 25 Cases

The evolving classification of rhabdomyosarcoma (RMS) now includes spindle cell RMS (SRMS). Bone/soft tissue SRMS often harbor TFCP2, or less often MEIS1 rearrangements. We studied 25 fusion-driven SRMS involving bone (n = 19) and soft tissue (n = 6). Osseous SRMS occurred in 13 women and 6 men (median age: 41 years) and involved the pelvis (5), sacrum (2), spine (4), maxilla (4), mandible (1), skull (1), and femur (2). Follow-up (median: 5 months) demonstrated local recurrence in 2/16 and distant metastases in 8/17 patients (median time to metastasis: 1 month). Eight patients died of disease; 9 were alive with disease. Soft tissue SRMS occurred in 4 men and 2 women (median: 50 years). Follow-up (median: 10 months) revealed distant metastasis at diagnosis (1), alive with unresected tumor (1), and no evidence of disease (4). Next-generation sequencing demonstrated FUS::TFCP2 (12), EWSR1::TFCP2 (3) and MEIS1::NCOA2 (2); FISH identified EWSR1 (2) rearrangements. Most TFCP2-rearranged SRMS (13/17) showed spindled/epithelioid morphology, rarely with rhabdomyoblasts. The bone tumors were diffusely desmin and MyoD1 positive with limited myogenin; 10/13 were ALK -positive and 6/15 were keratin positive. Soft tissue SRMS harbored EWSR1::TFCP2, MEIS1::NCOA2, ZFP64::NCOA2, MEIS1::FOXO1, TCF12::VGLL3 and DCTN1::ALK, and displayed spindled/epithelioid, leiomyomatous, and myxofibrosarcoma-like morphologies. Immunohistochemistry (IHC) was positive for MyoD1 (6/6), focal desmin (5/6), myogenin (3/6), and keratin (1/6). We conclude that TFCP2-rearranged SRMS of bone and soft tissue show consistent morphologic and IHC features, likely representing a distinct subset of RMS. Non-TFCP2 fusion-positive SRMS could represent a single RMS subset, multiple subtypes of RMS, or "fusion-defined" sarcomas with rhabdomyoblastic differentiation.

Lipoblastoma-Like Tumor and Fibrosarcoma-Like Lipomatous Neoplasm Represent the Same Entity: A Clinicopathologic and Molecular Genetic Study of 23 Cases Occurring in Both Men and Women at Diverse Locations

Lipoblastoma-like tumor (LLT) is a benign soft tissue tumor demonstrating mixed morphologic features of lipoblastoma, myxoid liposarcoma, and spindle cell lipoma but lacking genetic alterations associated with those tumors. LLT was originally thought to be specific to the vulva but has since been reported in the paratesticular region. The morphologic features of LLT overlap with those of "fibrosarcoma-like lipomatous neoplasm" (FLLN), a rare, indolent adipocytic neoplasm considered by some to form part of the spectrum of atypical spindle cell and pleomorphic lipomatous tumor. We compared the morphologic, immunohistochemical, and genetic features of 23 tumors previously classified as LLT (n = 17) and FLLN (n = 6). The 23 tumors occurred in 13 women and 10 men (mean age, 42 years; range, 17 to 80 years). Eighteen (78%) cases arose in the inguinogenital region, whereas 5 tumors (22%) involved noninguinogenital soft tissue, including the flank (n = 1), shoulder (n = 1), foot (n = 1), forearm (n = 1), and chest wall (n = 1). Microscopically, the tumors were lobulated and septated, with variably collagenized fibromyxoid stroma, prominent thin-walled vessels, scattered univacuolated or bivacuolated lipoblasts, and a minor component of mature adipose tissue. Using immunohistochemistry, 5 tumors (42%) showed complete RB1 loss, with partial loss in 7 cases (58%). RNA sequencing, chromosomal microarray, and DNA next-generation sequencing study results were negative for significant alterations. There were no clinical, morphologic, immunohistochemical, or molecular genetic differences between cases previously classified as LLT or FLLN. Clinical follow-up (11 patients [48%]; range, 2-276 months; mean, 48.2 months) showed all patients were alive without disease, and only one patient had experienced a single local recurrence. We conclude that LLT and FLLN represent the same entity, for which "LLT" seems most appropriate. LLT may occur in either sex and any superficial soft tissue location. Careful morphologic study and appropriate ancillary testing should allow for the distinction of LLT from its potential mimics.

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.

Anaplastic Kaposi Sarcoma: A Clinicopathologic and Molecular Genetic Analysis

Kaposi sarcoma (KS) is a human herpesvirus 8 (HHV8)-associated vascular proliferation that most often involves the skin. Rarely, KS shows marked nuclear atypia or pleomorphism; such examples are known as "anaplastic" KS. This poorly characterized variant often pursues an aggressive course; little is known of its genetic landscape. This study evaluated the clinicopathologic and genomic features of anaplastic KS. We identified 9 anaplastic KS cases from 7 patients and 8 conventional KS cases, including a matched conventional KS and primary metastasis anaplastic KS pair from a single patient (anaplastic KS diagnosed 9 years after conventional KS). All patients with anaplastic KS were men, aged 51 to 82 years, who had locally aggressive tumors predominantly affecting the soft tissue and bone of the lower extremities (5/7 patients). Four patients were known to be HIV positive (all on antiretrovirals), 2 were HIV negative, and 1 was of unknown HIV status. The tumors showed angiosarcoma-like or pleomorphic spindle cell sarcoma morphology. Plasma cell-rich chronic inflammation and hemosiderin deposition were commonly present. Single-nucleotide polymorphism-based chromosomal microarray analysis showed the anaplastic KS cohort to demonstrate highly recurrent whole chromosome (chr) gains of chr 7, 11, 19, and 21, which primarily affected olfactory and G protein-coupled receptor signaling and losses of chr6_q and chrY. Compared with conventional KS, anaplastic KS cases showed significantly more total copy number alterations and more frequent gains of chr7 and chr11_q13.1 (MARK2, RELA, and ESRRA, including high copy number gain in 1 case). Pathway analysis demonstrated that these gains preferentially affected genes that facilitate cyclin-dependent cell signaling. Furthermore, anaplastic KS cases were phylogenetically distinct from conventional KS cases, including the patient-matched primary metastasis anaplastic KS pair and conventional KS. Our study is the first to demonstrate that a more complex genome and distinct copy number alterations distinguish anaplastic KS from conventional KS. Gains of chr7 and chr11_q13.1 appear central to biological transformation.

Rhabdomyosarcoma Arising in Inflammatory Rhabdomyoblastic Tumor: A Genetically Distinctive Subtype of Rhabdomyosarcoma

"Inflammatory rhabdomyoblastic tumor" (IRMT) is a recently coined name for a distinctive soft tissue neoplasm characterized by slow growth, a dense histiocytic infiltrate, scattered, bizarre-appearing tumor cells with morphologic and immunohistochemical evidence of skeletal muscle differentiation, a near-haploid karyotype with retained biparental disomy of chromosomes 5 and 22, and usually indolent behavior. There are 2 reports of rhabdomyosarcoma (RMS) arising in IRMT. We studied the clinicopathologic and cytogenomic features of 6 cases of IRMT with progression to RMS. Tumors occurred in the extremities of 5 men and 1 woman (median patient age, 50 years; median tumor size, 6.5 cm). Clinical follow-up (6 patients: median, 11 months; range 4-163 months) documented local recurrence and distant metastases in 1 and 5 of 6 patients, respectively. Therapy included complete surgical resection (4 patients) and adjuvant/neoadjuvant chemo/radiotherapy (6 patients). One patient died of disease, 4 were alive with metastatic disease, and one was without evidence of disease. All primary tumors contained conventional IRMT. Progression to RMS appeared as follows: (1) overgrowth of monomorphic rhabdomyoblasts with diminished histiocytes, (2) monomorphic spindle cell morphology with variably pleomorphic rhabdomyoblasts and low mitotic activity, or (3) morphologically undifferentiated spindle cell and epithelioid sarcoma. All but one were diffusely desmin-positive, with more limited MyoD1/myogenin expression. All RMS arising in IRMT, either primary or metastatic, demonstrated widespread loss of heterozygosity with retained heterozygosity of chromosomes 5 and 20, and all but one displayed additional gains and losses involving loci containing oncogenes/ tumor suppressor genes, most often CDKN2A and CDKN2B. RMS arising in IRMT have unique clinicopathologic and cytogenomic features, warranting classification as a distinct, potentially aggressive RMS subtype. It should be distinguished from other RMSs, particularly fusion-driven spindle cell RMS and pleomorphic RMS.

Lack of radiosensitivity predicts poor disease specific survival in myxoid liposarcoma

BACKGROUND

Compared to other sarcomas, myxoid liposarcoma (ML) is known to be radiosensitive, with improved oncologic outcomes. Although these tumors "shrink" following radiotherapy, there is a paucity of data examining the degree of radiosensitivity and oncologic outcome. The purpose of the study was to evaluate pre- and postradiotherapy tumor volume to determine if size reduction impacts outcome.

METHODS

We reviewed 62 patients with ML undergoing surgical resection combined with preoperative radiotherapy, with pre- and postradiotherapy MRI. This included 34 (55%) males, with a mean age of 47 ± 14 years. All tumors were deep to the fascia, and 12 (19%) patients had tumors with a >5% round-cell component.

RESULTS

The mean volume reduction was 54% ± 29%. Compared to patients with >25% volume reduction, patients with reduction ≤25% had worse 10-year disease specific survival (86% vs. 37%, p < 0.01), in addition to an increased risk of metastatic disease (HR 4.63, p < 0.01) and death due to disease (HR 4.52, p < 0.01).

CONCLUSION

Lack of volume reduction is a risk factor for metastatic disease and subsequent death due to disease in patients with extremity ML treated with combined preoperative radiotherapy and surgery. This data could be used to stratify patients for adjuvant therapies and follow-up intervals.

Lymphangioleiomyomatosis in lymph node cytology: Another "Floating Island" to visit

Lymphangioleiomyomatosis (LAM) is a rare disease with variable presentations. The neoplastic cells in LAM demonstrate a unique and diagnostically important "myomelanocytic" phenotype. Cytologic reports of LAM are infrequent and have not in the past emphasized the floating island pattern in which circumscribed aggregates of lesional cells are rimmed by appliques of flattened endothelium. This case illustrates the cytology of LAM and emphasizes that the floating island cytoarchitectural pattern more classically associated with entities such as hepatocellular carcinomas may be seen in cytological preparations of LAM at unanticipated body sites.

"E-MGNET": Extra-Enteric Malignant Gastrointestinal Neuroectodermal Tumor- A Clinicopathological and Molecular Genetic Study of 11 Cases

Malignant gastrointestinal neuroectodermal tumors (MGNET), also known as "gastrointestinal clear cell sarcoma-like tumor", are very rare, aggressive sarcomas characterized by enteric location, distinctive pathologic features, and EWSR1/FUS::ATF1/CREB1 fusions. Despite identical genetics, the clinicopathologic features of MGNET are otherwise quite different from clear cell sarcoma of soft parts (CCS). Only exceptional extra-enteric MGNET (E-MGNET) have been reported. We report a series of 11 E-MGNET, the largest to date. Cases diagnosed as MGNET and occurring in non-intestinal locations were retrieved. Clinical follow-up was obtained. The tumors occurred in 3 males and 8 females (14-70 years of age, median 33 years) and involved the soft tissues of the neck (3), shoulder (1), buttock (2), orbit (1), and tongue/parapharyngeal space (1), the urinary bladder (1) and the falciform ligament/liver (1). Tumors showed morphologic features of enteric MGNET (small, relatively uniform, round to ovoid cells with round, regular nuclei containing small nucleoli, growing in multinodular and vaguely lobular patterns, with solid, pseudoalveolar and pseudopapillary architecture). Immunohistochemical results were: S100 protein (11/11), SOX10 (11/11), synaptophysin (3/10), CD56 (7/9), CD117 (3/9), DOG1 (0/4), ALK (4/8), chromogranin A (0/10), HMB45 (0/11), Melan-A (0/11), tyrosinase (0/4), MiTF (0/11). NGS results were: EWSR1::ATF1 (7 cases), EWSR1::CREB1 (3 cases) and EWSR1::PBX1 (1 case). The EWSR1::PBX1-positive tumor was similar to other cases, including osteoclast-like giant cells, and negative for myoepithelial markers. Clinical follow-up (range: 10 to 70 months; median 34 months) showed 4 patients dead of disease (10.5, 12, 25 and 64 months after diagnosis), 1 patient alive with extensive metastases (43 months after diagnosis), 1 patient alive with persistent local disease (11 months after diagnosis), and 4 alive without disease (10, 47, 53 and 70 months after diagnosis). One case is too recent for follow-up. The clinicopathologic and molecular genetic features of rare E-MGNET are essentially identical to those occurring in intestinal locations. Otherwise-typical E-MGNET may harbor EWSR1::PBX1, a finding previously unreported in this tumor type. As in enteric locations, the behavior of E-MGNET is aggressive, with metastases and/or death from disease in at least 50% of patients. E-MGNET should be distinguished from CCS and other tumors with similar fusions. ALK expression appears to be a common feature of tumors harboring EWSR1/FUS::ATF1/CREB1 fusion but is unlikely to predict therapeutic response to ALK inhibition. Future advances in our understanding of these unusual tumors will hopefully lead to improved nomenclature.

Gastrointestinal Glomus Tumors: A Single Institution, 20-Year Retrospective Study

INTRODUCTION

Glomus tumors are rare mesenchymal neoplasms composed of cells resembling those of the thermoregulatory glomus body, typically occurring in the skin and superficial soft tissues. Rarely do they occur in the gastrointestinal tract, in particular the stomach, where they have been the subject of case reports and small series. We present our institutional experience with gastrointestinal glomus tumors.

METHODS

A retrospective review of all gastrointestinal glomus tumors was conducted across all three Mayo Clinic sites in Minnesota, Arizona, and Florida from 2001 to 2021. Patient characteristics, pathologic findings, imaging features, operative reports, and clinical outcomes were abstracted. Descriptive statistics were utilized to report outcomes.

RESULTS

Nine patients with glomus tumors were identified (five men and four women). The median age was 53 [interquartile range (IQR), 44-69] y. Four patients presented with abdominal discomfort, three had anemia or bleeding, and two tumors were incidentally diagnosed. Computed tomography scans identified masses thought to represent gastrointestinal stromal tumors or neuroendocrine tumors in all patients. The tumors were localized to the stomach in all cases, specifically in the gastric antrum. Seven patients underwent preoperative endoscopy, including five with endoscopic ultrasonography. Endoscopic biopsies were interpreted as glomus tumors (n = 3), neuroendocrine tumors (n = 2), and nondiagnostic (n = 2). All patients underwent open (n = 3) or minimally invasive (n = 6) margin-negative resection by wedge resection (n = 5) or distal gastrectomy (n = 4). No nodal metastases were identified radiographically or on pathologic examination. The median tumor size was 2.5 [IQR 1.3-3.4] cm. All tumors showed at least in part typical glomus tumor morphology and smooth muscle actin expression. Aberrant synaptophysin expression was present in the two tumors initially classified as NET. Using the current WHO criteria, tumors were classified as histologically malignant (n = 1) and of "uncertain malignant potential" (n = 8). At a median follow-up of 15 [IQR 1-56] mo, all patients were asymptomatic and without recurrence. Two patients died of unrelated causes. No patients received adjuvant therapies.

CONCLUSIONS

Our 20-year, single institution, 3-site experience with resected gastrointestinal glomus tumors suggests the rarity, predisposition to involve the gastric antrum, and potentially an indolent clinical behavior of many of these tumors. Long-term follow-up is warranted as some previously reported gastric glomus tumors have metastasized, including cases lacking morphologic evidence of malignancy. Surgical resection, with minimally invasive wedge resection alone, is likely sufficient for the management of most gastric glomus tumors.

Metastatic melanoma involving a genetically confirmed angiofibroma of soft tissue: A previously unreported type of tumor-to-tumor metastasis

Tumor-to-tumor metastases are an uncommon phenomenon and are very rare in the context of malignant melanoma. This case report describes a 73-year-old male who underwent an excision of a melanoma from his forehead. Six months later, he developed metastatic disease, including metastasis to a genetically confirmed angiofibroma of soft tissue of the abdominal wall. Angiofibroma of soft tissue is a relatively recently described benign fibrovascular soft tissue tumor, and there appear to be no previous reports of it being a recipient tumor for a metastasis. Awareness of the phenomenon of tumor-to-tumor metastasis and of the distinctive morphologic and molecular genetic features of angiofibroma are critical to avoid misdiagnosis of this very rare event as "dedifferentiated" melanoma.

Pleomorphic Liposarcoma: A Series of 120 Cases With Emphasis on Morphologic Variants

Pleomorphic liposarcoma (PLPS) is a highly aggressive sarcoma comprising variable numbers of pleomorphic lipoblasts mixed with undifferentiated pleomorphic sarcoma (UPS)-like areas. Morphologic variants, such as myxofibrosarcoma-like or epithelioid, may cause diagnostic confusion, especially on a core biopsy, but there are few data on the prognostic significance of these features. A total of 120 PLPS biopsies and resection specimens were reviewed and catalogued based on the presence of myxofibrosarcoma-like, UPS-like, and epithelioid foci, in 10% increments. The clinical parameters were collected. Cases occurred in 75 males and 45 females, ranging from 8 to 98 years (median, 62.5 y). Cases arose in the extremities (n=72), trunk (n=32), head/neck (n=10), bone (n=4), mediastinum (n=1), or viscera (colon polyp, n=1). Of those with known depth (n=81), 40 were intramuscular, 34 were subcutaneous, and 7 arose in the dermis. Their sizes ranged from 1 to 24.5 cm (median, 7 cm). Of the patients with ≥1 month of follow-up (n=70), 5 had recurrence and 15 had metastasis. The 5-year overall survival and event-free survival rates were 66.2% and 63.1%, respectively. Tumors ≥5 cm had inferior overall survival compared with tumors <5 cm. The presence of epithelioid areas was also statistically significant in terms of poorer overall survival and event-free survival, while tumors with ≥50% undifferentiated pleomorphic-like areas had better overall survival. There was a trend towards poorer outcomes in tumors with necrosis (≥1%). PLPS is an aggressive adipocytic malignancy that is most commonly present in the extremities of older adults. The morphologic features of these tumors are diverse, and they may be mistaken for UPS or myxofibrosarcoma, carcinoma, and melanomas, particularly on biopsies. Tumor size, necrosis, and epithelioid morphology are associated with adverse prognosis.

Malignant Melanotic Nerve Sheath Tumor

Malignant melanotic nerve sheath tumors are uncommon pigmented tumors of Schwann cell origin, most often found along the spinal nerves. Although well-described in the literature, the tumors are quite rare, making up <1% of nerve sheath tumors. Physicians are, therefore, often unfamiliar with both the appearance and the optimal treatment of such tumors. Morphologically, many imaging features overlap with schwannomas and neurofibromas. Nevertheless, the malignant melanotic nerve sheath tumors are crucial to identify. They can be extremely aggressive, and the management of these tumors is considerably different from their benign counterparts. In this radiology-pathology review, we will highlight the imaging appearance, histologic features, surgical resection, and subsequent therapeutic strategies in a patient with a lumbar malignant melanotic nerve sheath tumor.

Radiation-associated angiosarcoma of the breast with initial presentation as non-mass enhancement on MRI

Radiation-associated angiosarcoma of the breast (RAASB) is a rare and aggressive malignancy occurring after radiation therapy as part of breast cancer treatment. RAASB usually presents several years after prior radiation and typically involves the skin with or without involvement of the parenchyma. Most RAASB are detected as cutaneous changes on physical exam. Herein, we present a unique case of a clinically occult RAASB diagnosed as non-mass enhancement on annual surveillance breast MRI.

Overlapping morphological, immunohistochemical and genetic features of superficial CD34-positive fibroblastic tumor and PRDM10-rearranged soft tissue tumor

Superficial CD34-positive fibroblastic tumor (SCD34FT) is a recently recognized soft tissue tumor that is considered to be of borderline malignancy. The pathogenesis of this tumor remains incompletely understood, but it has been suggested that SCD34FT overlaps with tumors showing fusions involving the PRDM10 gene. Previous analyses of PRDM10-rearranged tumors have demonstrated that they have a distinct gene expression profile, resulting in high expression of CADM3 (also known as SynCam3), which can be detected immunohistochemically. Here, we investigated a series (n = 43) of SCD34FT or PRDM10-rearranged tumors and potential mimics (n = 226) with regard to morphological, genetic, and immunohistochemical features. The results show that SCD34FT and PRDM10-rearranged tumor are morphologically indistinguishable; 41 of 43 tumors of both entities are CADM3-positive. Hence, we suggest that they constitute a single entity, preferably referred to as SCD34FT. Expression of CADM3 was only rarely seen in other soft tissue tumors, except in tumors with Schwann cell differentiation. Thus, IHC for CADM3, in combination with the characteristic morphological features, is a valuable adjunct in the diagnosis of SCD34FT.

Cellular Variant of Kaposiform Lymphangiomatosis: A Report of Three Cases, Expanding the Morphologic and Molecular Genetic Spectrum of this Rare Entity

Kaposiform lymphangiomatosis (KLA) is a very rare form of generalized lymphatic anomaly, consisting of a diffuse proliferation of abnormal, dilated lymphatics and small fascicles of hemosiderin-laden spindled lymphatic endothelial cells. KLA occurs in children and young adults and may present with multicentric disease, pleural and pericardial effusions, and life-threatening coagulopathy. Genetically, KLA most often harbor somatic activating mutations in NRAS. We recently encountered 3 cases of KLA with cellular features, resembling kaposiform hemangioendothelioma (KHE) and studied their clinicopathologic, radiologic and molecular genetic features. The patients (1 male, 2 females; ages 2 years, 2 months, 4 years) presented with multicentric disease involving skin, soft tissue, bone and spleen, and thrombocytopenia/coagulopathy. Advanced imaging studies confirmed multicentric disease. Biopsies (skin, soft tissue, bone, spleen) demonstrated both conventional KLA and much more cellular foci, consisting of sheets, nodules, glomeruloid structures, and "sieve-like" arrays of lymphatic endothelial cells (positive for CD31 and D2-40). Cellular areas superficially resembled KHE but displayed more epithelioid cytology and lacked surrounding hyaline fibrosis and minute platelet aggregates. Molecular genetic studies demonstrated NRAS c.181C>A p.Q61K (Gln61Lys) in 2 specimens from one patient and HRAS p.A59_Q61delinsGGSIL in another. Two patients were treated with sirolimus; all are currently alive with stable disease. We conclude that cellular morphology in KLA, a previously undescribed feature, does not appear to be associated with clinical features, site of disease, mutation type, response to sirolimus, or outcome. Although cellular KLA may mimic KHE, there are sufficient clinical, morphologic, and genetic differences such that these are likely unrelated diseases.

Myxoid pleomorphic liposarcoma-a clinicopathologic, immunohistochemical, molecular genetic and epigenetic study of 12 cases, suggesting a possible relationship with conventional pleomorphic liposarcoma

Myxoid pleomorphic liposarcoma is a recently defined subtype of liposarcoma, which preferentially involves the mediastinum of young patients and shows mixed histological features of conventional myxoid liposarcoma and pleomorphic liposarcoma. While myxoid pleomorphic liposarcoma is known to lack the EWSR1/FUS-DDIT3 fusions characteristic of the former, additional genetic data are limited. To further understand this tumor type, we extensively examined a series of myxoid pleomorphic liposarcomas by fluorescence in situ hybridization (FISH), shallow whole genome sequencing (sWGS) and genome-wide DNA methylation profiling. The 12 tumors occurred in 6 females and 6 males, ranging from 17 to 58 years of age (mean 33 years, median 35 years), and were located in the mediastinum (n = 5), back, neck, cheek and leg, including thigh. Histologically, all cases consisted of relatively, bland, abundantly myxoid areas with a prominent capillary vasculature, admixed with much more cellular and less myxoid foci containing markedly pleomorphic spindled cells, numerous pleomorphic lipoblasts and elevated mitotic activity. Using sWGS, myxoid pleomorphic liposarcomas were found to have complex chromosomal alterations, including recurrent large chromosomal gains involving chromosomes 1, 6-8, 18-21 and losses involving chromosomes 13, 16 and 17. Losses in chromosome 13, in particular loss in 13q14 (including RB1, RCTB2, DLEU1, and ITM2B genes), were observed in 4 out of 8 cases analyzed. Additional FISH analyses confirmed the presence of a monoallelic RB1 deletion in 8/12 cases. Moreover, nuclear Rb expression was deficient in all studied cases. None showed DDIT3 gene rearrangement or MDM2 gene amplification. Using genome-wide DNA methylation profiling, myxoid pleomorphic liposarcomas and conventional pleomorphic liposarcomas formed a common methylation cluster, which segregated from conventional myxoid liposarcomas. While the morphologic, genetic and epigenetic characteristics of myxoid pleomorphic liposarcoma suggest a link with conventional pleomorphic liposarcoma, its distinctive clinical features support continued separate classification for the time being.

EWSR1-WT1 gene fusions in neoplasms other than desmoplastic small round cell tumor: a report of three unusual tumors involving the female genital tract and review of the literature

Desmoplastic small round cell tumor (DSRCT) is a high-grade round cell sarcoma that typically arises in the abdominopelvic cavity of young males, co-expresses keratins and desmin, and carries a pathognomonic EWSR1-WT1 gene fusion. The EWSR1-WT1 gene fusion is generally considered specific for DSRCT, although there are two reports of this fusion in tumors otherwise lacking features of DSRCT. We report three female genital tract tumors with EWSR1-WT1 fusions but showing morphologic and immunohistochemical features incompatible with DSRCT. The tumors occurred in the uterine cervix, uterine corpus/ovaries, and vagina, respectively, of 46, 30, and 20-year-old women. Two tumors consisted of a sheet-like to fascicular proliferation of relatively uniform spindled to occasionally more epithelioid cells arrayed about thick-walled, hyalinized, and capillary-sized vessels, with distinctive areas of pseudovascular change, and absence of desmoplastic stroma. The third tumor resembled a monomorphic spindle cell sarcoma with necrosis. All had diffuse desmin and variable but more limited keratin expression, two of three expressed smooth muscle actin, and all were negative for h-caldesmon, CD10, estrogen receptor, myogenin, N-terminus WT-1, and S100 protein. One patient received neoadjuvant chemotherapy and radiation therapy followed by resection and is disease-free 42 months after diagnosis. Another patient was managed by resection only and is disease-free 9 months after initial diagnosis. The remaining patient recently underwent resection of multifocal pelvic disease. Comprehensive differential gene expression analysis on two tumors compared to two classic DSRCTs with known EWSR1-WT1 fusions resulted in 1726 genes that were differentially expressed (log2 fold change >2 or < -2) and statistically significant (FDR < 5%). In combination with previous reports, our findings suggest pleiotropy of the EWSR1-WT1 fusion is possible and not limited to DSRCT. Subsets of non-DSRCT EWSR1-WT1 positive tumors may represent discrete entities, but further study is necessary.

Head and Neck Low-Grade Fibromyxoid Sarcoma: A Clinicopathologic Study of 15 Cases

Low-grade fibromyxoid sarcoma (LGFMS) is an uncommon mesenchymal tumor usually arising in the lower extremities and trunk. Only rare examples in the head and neck region have been reported. Fifteen cases of head and neck LGFMS were retrieved. MUC4 was performed on all cases. Results for smooth muscle actins, β-catenin, desmin, S100 protein, Epithelial membrane antigen (EMA) and STAT6 immunohistochemistry, as well as FUS rearrangement status, were recorded when available. Sites included neck (8), supraclavicular region (4) and orbit (1), parapharyngeal space (1) and lower lip (1). The age of the patients ranged from 3 to 97 years (median, 26 years). Tumors displayed classical morphologic features of LGFMS, as described. All cases (15/15) were positive for MUC4, and all cases tested (4/4) harbored FUS rearrangement. Variable positivity for EMA was identified in one case. Follow-up was available in 11 patients, ranging from 2 to 240 months (mean 71.4 months; median, 44 months). Three tumors recurred locally; none metastasized. In conclusion, although distinctly uncommon, LGFMS may arise in the head and neck region and should be distinguished from other more common spindle cell tumors in these locations. The morphologic, immunohistochemical and molecular genetic features of head/neck LGFMS are identical to those occurring elsewhere. The long-term metastatic risk of LGFMS in these locations remains to be fully elucidated.

Rapidly fatal SMARCA4-deficient undifferentiated sarcoma originating from hybrid hemosiderotic fibrolipomatous tumor/pleomorphic hyalinizing angiectatic tumor of the foot

Pleomorphic hyalinizing angiectatic tumor (PHAT) of soft parts and hemosiderotic fibrolipomatous tumor (HFLT) are two rare low-grade locally recurring neoplasms with predilection for the foot/ankle. Recent studies support a close link between the two entities, and origin of PHAT from HFLT and occurrence of hybrid HFLT/PHAT have been documented. Both lesions often harbor TGFBR3 or MGEA5 rearrangements. Rare sarcomas originating from HFLT/PHAT have been reported, typically resembling myxofibrosarcoma or myxoinflammatory fibroblastic sarcoma. We describe a novel SMARCA4-deficient undifferentiated sarcoma with rhabdoid features originating from hybrid HFLT/PHAT in the foot of a 54-year-old male. The tumor pursued a highly aggressive course with rapid regrowth after resection and multiple metastases resulting in patient's death within 5 months, despite systemic chemotherapy. Immunohistochemistry revealed SMARCA4 loss in the undifferentiated sarcoma, but not in the HFLT/PHAT. Molecular testing confirmed TGFBR3/MGEA5 rearrangements. This report expands the phenotypes of sarcomas developing from pre-existing PHAT/HFLT.

NUTM1-rearranged colorectal sarcoma: a clinicopathologically and genetically distinctive malignant neoplasm with a poor prognosis

NUTM1 gene rearrangements were originally identified in NUT carcinoma. Recently, NUTM1 has been discovered to rearrange with a variety of gene partners in malignancies of diverse location and type. Only one NUTM1-rearranged tumor occurring in the colon has been reported. Herein we report five such tumors. The five tumors occurred in four females and one male, ranging from 38 to 67 years of age (median 51 years). The masses occurred in the colon (cecum, descending, sigmoid) and ileocecal valve region, measuring 2.5-20 cm in size (median 7 cm). Four patients had metastases at presentation (liver, n = 4; lymph nodes, n = 3). Histologically, the lesions arose in the submucosa, infiltrating into the mucosa and muscularis propria, and grew in fibrosarcoma-like fascicles and sheets of epithelioid or rhabdoid cells, with foci of hyalinized to vaguely osteoid-like matrix. The tumors were composed of relatively monomorphic, spindled to epithelioid cells with focal rhabdoid morphology, hyperchromatic nuclei, and small nucleoli. Mitotic activity was usually low (range 1-14/10 HPF; median 5/10 HPF); necrosis was present in two cases. Variable keratin expression and uniform nuclear NUT expression was present; KIT/DOG1 were negative and SMARCB1/SMARCA4 were retained. Next-generation sequencing identified MXD4-NUTM1 rearrangement in all cases (breakpoints: MXD4 exon 5, NUTM1 exons 2 or 3). Follow-up showed one of the four patients who presented with metastases to be dead of disease at 30 months; the other three patients were alive with metastatic disease. The final patient is disease-free, 5 months after diagnosis. NUTM1-rearranged colorectal sarcomas have characteristic morphologic, immunohistochemical, and molecular genetic features, suggesting that they represent a distinct entity within the family of NUTM1-rearranged neoplasia. A NUTM1-rearranged tumor should be considered for any difficult-to-classify submucosal spindle cell neoplasm of the gastrointestinal tract, in particular keratin-positive tumors showing an unusual combination of fibrosarcomatous, epithelioid to rhabdoid and hyalinized morphologies. Recognition of MXD4-NUTM1 rearranged sarcomas may be therapeutically important, even though best treatment is currently elusive/unknown.

Glomangiomatosis of the Upper Extremity

We describe a 43-year-old woman with a 23-year history of recurrent extradigital glomus tumors (glomangiomatosis) of the hand and forearm. She presented with a typical presentation of pain, tenderness to palpation, and hypersensitivity of the affected regions. After surgical resection, she continued to present with new locations of tumor burden and progressively malignant features of the tumors. This exceedingly rare presentation highlights the importance of vigilantly monitoring patients for recurrence with glomangiomatosis.

Eccrine angiomatous hamartoma: First case in the cytology literature

A 34-year-old male presented with a swelling on the volar surface of the third digit of his right hand. This swelling was associated with pain and erythema. Ultrasound-guided needle biopsy was performed. Cytologic and histologic preparations together confirmed the diagnosis of a rarely encountered mixed epithelial and mesenchymal proliferation, an eccrine angiomatous hamartoma. To our knowledge, this case is the first to illustrate the cytomorphologic features of this rare lesion.

PRRX1-NCOA1-rearranged fibroblastic tumour: a clinicopathological, immunohistochemical and molecular genetic study of six cases of a potentially under-recognised, distinctive mesenchymal tumour

AIMS

PRRX1-NCOA1-rearranged fibroblastic tumour is a recently described, rare mesenchymal tumour. Only four cases have been previously reported. The aim of this article is to report six additional cases of this unusual mesenchymal neoplasm, with an emphasis on its differential diagnosis.

METHODS AND RESULTS

The six cases were from three females and three males (age, 20-49 years; median, 42 years). Three tumours were located on the abdominal wall; two from the shoulder/axillary areas, and one on the lateral hip. All presented as slow-growing subcutaneous nodules, ranging from 26 to 55 mm (median, 40 mm). The tumours consisted of circumscribed, variably cellular nodules composed of relatively bland plump spindled to epithelioid cells arranged singly, in cords, and occasionally in nests, embedded in hyalinised and collagenous stroma. Small hypocellular myxoid zones with ropey collagen fibres were present, as were irregularly dilated, gaping, crescent-shaped or staghorn-like thin-walled vessels, best appreciated at the periphery. Immunohistochemistry for CD34, S100, MUC4 and STAT6 was consistently negative. RNA-sequencing revealed PRRX1-NCOA1 fusions in all cases. Of the four cases with limited follow-up (1.5-4 months), none recurred following local surgical excision.

CONCLUSIONS

The morphological features of PRRX1-NCOA1-rearranged fibroblastic tumour overlap with those of RB1-deficient soft-tissue tumours, solitary fibrous tumour, and low-grade fibromyxoid sarcoma/sclerosing epithelioid fibrosarcoma. This differential diagnosis can be resolved with a combination of careful morphological study and the application of a panel of immunostains, although molecular genetic study is most definitive. The natural history of PRRX1-NCOA1-rearranged fibroblastic tumour appears to be quite favourable, although longer-term study of a larger number of cases is warranted.

RNAscope CSF1 chromogenic in situ hybridization: a potentially useful tool in the differential diagnosis of tenosynovial giant cell tumors

Colony stimulating factor-1 (CSF1) upregulation and CSF1/colony-stimulating factor 1 receptor (CSF1R) signaling pathway is central to the tumorigenesis of tenosynovial giant cell tumors (TGCT) of both localized (LTGCT) and diffuse (DTGCT) types, and has been demonstrated in a small number of malignant tumors (MTGCT) as well. In situ hybridization for CSF1 mRNA has been shown to be potentially useful in the diagnosis of TGCT, although only a relatively small number of cases have been studied. We studied CSF1 mRNA expression using RNAscope chromogenic in situ hybridization (CISH) in standard tissue sections from 31 TGCT and 26 non-TGCT, and in tumor microarray slides (Pantomics normal MN0341, Pantomics tumor MTU391, Pantomics melanoma MEL961). Among normal tissues, CSF1 mRNA expression was invariably present in synovium (10/10, 100%) and absent in all other normal tissues. All LTGCT and DTGCT were positive (24/24, 100%), exclusively in large, eosinophilic synoviocytes. MTGCT contained large clusters of CSF1-positive malignant synoviocytes (8/8, 100%); malignant spindled cells were also positive. Among non-TGCT, CSF1 CISH was less often positive with high specificity (90%). CSF1-positive cases included leiomyosarcoma, giant cell tumor of bone and of soft parts, pulmonary carcinoma and others. The sensitivity and specificity of RNAscope CSF1 mRNA CISH for the diagnosis of TGCT were 100% and 90%, respectively. We conclude that RNAscope CSF1 CISH may be a valuable adjunct for the diagnosis of TGCT of all types, especially those with atypical or malignant morphologic features. Detection of CSF1 mRNA expression may also have predictive significance in cases where use of the CSF1 inhibitor pexidartinib is considered.

CD10 (neprilysin) expression: a potential adjunct in the distinction of hibernoma from morphologic mimics

Although the morphologic diagnosis of hibernoma is usually straightforward, some hibernomas have atypical morphologic features, mimicking atypical lipomatous tumors/well-differentiated liposarcomas (ALT/WDLs). In addition, the multivacuolated brown fat cells may be mistaken for lipoblasts by pathologists, especially those without significant soft tissue tumor exposure. Thus, we continue to receive in consultation cases of hibernoma sent for MDM2 fluorescence in situ hybridization testing to exclude ALT/WDL. Testing hibernomas for MDM2 amplification, however, adds cost and delays the final diagnosis. Recently, we have noted expression of neprilysin (CD10, CALLA), a zinc-dependent metalloproteinase involved in the inactivation of various peptide hormones, in brown fat cells, and wished to explore the potential utility of this widely available, inexpensive ancillary test in the differential diagnosis of hibernoma. Formalin-fixed, paraffin-embedded tissue sections from well-characterized cases of hibernoma (n = 48), brown fat (n = 21), ALTs/WDLs (n = 17), pleomorphic liposarcomas (PLPSs) (n = 6), lipomas (n = 5), and fat necrosis (n = 5) were immunostained for CD10, using a commercially available antibody and routine laboratory protocols. CD10 expression was evaluated in both adipocytes and in surrounding stromal cells. The hibernomas occurred in 28 men and 20 women, ranging from 11 to 76 years of age and involved the extremities (n = 25), pelvis (n = 7), abdomen/pelvis/retroperitoneum (n = 7), head and neck region (n = 6), back (n = 2), and chest (n = 1). All showed diffuse, strong CD10 expression in multivacuolated brown fat cells and in the majority of adjacent univacuolated fat cells. Brown adipose tissue from various anatomic structures showed an identical pattern of immunoreactivity. In contrast, CD10 expression was present in the adipocytes of only 3 of 17 (18%) ALTs/WDLs and was absent in lipomas and fat necrosis. Lipoblasts expressed CD10 in 3 PLPSs. Expression of CD10 by surrounding fibroblastic stromal cells was more widespread, present in 13 hibernomas, 10 ALTs/WDLs, 1 instance of fat necrosis, 6 PLPSs, and 4 examples of brown fat. We conclude that immunohistochemistry for CD10 may represent a useful, rapid and inexpensive ancillary test in the differential diagnosis of hibernoma from potential morphologic mimics, especially when morphologic features favor hibernoma. CD10 expression in adipocytes, however, should be rigorously distinguished from fibroblastic stromal cell CD10 expression, a nonspecific finding.

Mesenchymal tumors of the gastrointestinal tract with NTRK rearrangements: a clinicopathological, immunophenotypic, and molecular study of eight cases, emphasizing their distinction from gastrointestinal stromal tumor (GIST)

Mesenchymal tumors driven by NTRK fusions are clinically and morphologically heterogeneous. With an increasing number of clinicopathological entities being associated with NTRK fusions, the diagnostic and predictive value of the identification of NTRK fusions is uncertain. Recently, mesenchymal tumors in the gastrointestinal tract with NTRK fusions were described as gastrointestinal stromal tumors (GIST), but the nosology of such neoplasms remains controversial. We report eight mesenchymal tumors involving the gastrointestinal tract with NTRK1 or NTRK3 rearrangements. The tumors occurred in six children and two adults, five males and three females (age range 2 months-55 years; median 3.5 years), and involved the small intestine (n = 4), stomach (n = 2), rectum (n = 1), and mesentery (n = 1). Clinical outcomes were variable, ranging from relatively indolent (n = 2) to aggressive diseases (n = 2). Morphologically, the tumors were heterogeneous and could be classified in the following three groups: (1) infantile fibrosarcoma involving the gastrointestinal tract (n = 4), enriched for NTRK3 fusions; (2) low-grade CD34-positive, S100 protein-positive spindle-cell tumors, associated with NTRK1 fusions (n = 2); and (3) unclassified high-grade spindle-cell sarcomas, with NTRK1 fusions (n = 2). By immunohistochemistry, the tumors demonstrated diffuse pan-TRK expression, of variable intensity, and lacked a specific line of differentiation. Four cases expressed CD34, which was coexpressed with S100 protein in three cases. Expression of SOX10, KIT, and DOG1 was consistently absent. Molecular genetic testing identified TPM3-NTRK1 (n = 3), TPR-NTRK1, LMNA-NTRK1, and ETV6-NTRK3 (n = 2), and SPECC1L-NTRK3 in-frame gene fusions. We conclude that the evaluation of mesenchymal spindle-cell neoplasms of the gastrointestinal tract without a definitive line of differentiation should include interrogation of NTRK alterations, particularly in pediatric patients. Mesenchymal tumors of the gastrointestinal tract with NTRK rearrangements are clinically and morphologically heterogeneous, and few, if any, seem related to GIST.

Hiding in plain sight: Gene panel and genetic markers reveal 26-year undiagnosed tumor-induced osteomalacia of the rib concurrently misdiagnosed as X-linked hypophosphatemia

Tumor-induced osteomalacia (TIO), caused by phosphaturic mesenchymal tumors (PMTs), is a rare paraneoplastic syndrome characterized by frequent bone fractures, bone pain, muscle weakness, and affected gait. These tumors typically secrete high levels of Fibroblastic Growth Factor 23 (FGF23), a hormone which acts on the kidney to cause hypophosphatemia, ultimately impairing bone mineralization. In this case report, we present a 41-year-old female with FGF23-mediated hypophosphatemia with a 26-year delay in TIO diagnosis and a concurrent misdiagnosis of X-linked hypophosphatemic rickets (XLH). Given an absence of family history of hypophosphatemia, a 13-gene hypophosphatemia panel including XLH (PHEX gene) was performed and came back negative prompting a diagnostic search for a PMT causing TIO. A ⁶⁸Ga-DOTATATE PET/CT scan revealed the presence of a 9th right rib lesion, for which she underwent rib resection. The patient's laboratory values (notably serum phosphorus, calcium, and vitamin D) normalized, with FGF23 decreasing immediately after surgery, and symptoms resolving over the next three months. Chromogenic in situ hybridization (CISH) and RNA-sequencing of the tumor were positive for FGF23 (CISH) and the transcriptional marker FN1-FGFR1, a novel fusion gene between fibronectin (FN1) and Fibroblast Growth Factor Receptor 1 (FGFR1), previously determined to be present in the majority of TIO-associated tumors. This case demonstrates the notion that rare and diagnostically challenging disorders like TIO can be undiagnosed and/or misdiagnosed for many years, even by experienced clinicians and routine lab testing. It also underscores the power of novel tools available to clinicians such as gene panels, CISH, and RNA sequencing, and their ability to characterize TIO and its related tumors in the context of several phenotypically similar diseases.

Update on SWI/SNF-related gynecologic mesenchymal neoplasms: SMARCA4-deficient uterine sarcoma and SMARCB1-deficient vulvar neoplasms

Our knowledge regarding the role of genes encoding the chromatin remodeling switch/sucrose non-fermenting (SWI/SNF) complex in the initiation and progression of gynecologic malignancies continues to evolve. This review focuses on gynecologic tumors in which the sole or primary genetic alteration is in SMARCA4 or SMARCB1, two members of the SWI/SNF chromatin remodeling complex. In this review, we present a brief overview of the classical example of such tumors, ovarian small cell carcinoma of hypercalcemic type, and then a detailed review and update of SMARCB1-deficient and SMARCA4-deficient tumors of the uterus and vulva.

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.

Treatment outcome of superficial leiomyosarcoma

BACKGROUND

Nonuterine leiomyosarcomas (LMS) are common extremity soft-tissue sarcomas. Deep LMS are at an increased risk for recurrence; however, few studies have focused on superficial LMS.

METHODS

We reviewed the clinicopathological features of 82 patients with a primary superficial LMS. The mean age and follow-up were 57 ± 15 and 7 ± 5 years. Depth was classified as dermal (based in the skin; n = 35, 43%) and subcutaneous (based below the dermis, above the fascia; n = 47, 57%) on the final resection specimen. Dermal cases were treated with negative margin resection, while subcutaneous tumors were evaluated by a multidisciplinary team for consideration of possible adjuvant therapy.

RESULTS

The 10-year disease-specific survival (DSS) for superficial LMS was 90% with no difference (p = .18) in the 10-year DSS between patients with dermal (100%) and subcutaneous (86%) LMS. All disease recurrences occurred in subcutaneous LMS (17% vs. 0%, p = .02) and subcutaneous tumors had a worse10-year metastatic free survival (81% vs. 100%, p = .03).

CONCLUSIONS

The results of this study suggest that dermal LMS can be managed with a negative margin resection alone. Although the prognosis for patients with subcutaneous LMS is quite favorable, there is some risk for local and distant recurrence, and such patients will benefit from multidisciplinary care.