Histiocytic sarcoma, a rare malignant neoplasm showing morphologic and immunophenotypic features of histiocytes, is characterized typically by extranodal presentation and a dismal clinical course, ...particularly in patients with disseminated disease. A history of hematolymphoid disorder can be identified in a subset of patients, suggesting transdifferentiation of a preexisting hematolymphoid neoplasm in its pathogenesis. The differential diagnosis of histiocytic sarcoma includes various lymphomas, other histiocytic and dendritic cell neoplasms, carcinomas, melanomas, and pleomorphic sarcomas. Given its rarity and histologic overlap with diverse mimics, the diagnosis of histiocytic sarcoma can be extremely challenging. Recognition of morphologic clues, as well as judicious application of immunohistochemical markers to confirm its histiocytic lineage and to exclude mimics, is crucial for the diagnosis. Recent molecular studies by targeted next-generation sequencing identified recurrent alterations in the mitogen-activated protein (MAP) kinase pathway and chromatin regulators in the pathogenesis of histiocytic sarcoma and may suggest possible therapeutic targets.
Pseudomyogenic (epithelioid sarcoma-like) hemangioendothelioma is a distinctive vascular neoplasm of intermediate biological potential with a predilection for young adults and frequent multifocal ...presentation. Pseudomyogenic hemangioendothelioma is characterized by loose fascicles of plump spindled and epithelioid cells with abundant eosinophilic cytoplasm and coexpression of keratins and endothelial markers. Recently, a SERPINE1-FOSB fusion has been identified as a consistent genetic alteration in pseudomyogenic hemangioendothelioma. FOSB gene fusions have also been reported in a subset of epithelioid hemangiomas. The purpose of this study was to assess the potential diagnostic utility of FOSB immunohistochemistry for pseudomyogenic hemangioendothelioma compared with other endothelial neoplasms and histologic mimics. We evaluated whole-tissue sections from 274 cases including 50 pseudomyogenic hemangioendotheliomas, 84 other vascular tumors (24 epithelioid hemangiomas including 6 cases with angiolymphoid hyperplasia with eosinophilia histology, 20 epithelioid angiosarcomas, 20 epithelioid hemangioendotheliomas 17 CAMTA1 positive, 2 TFE3 positive, 10 spindle-cell angiosarcomas, and 10 epithelioid angiomatous nodules), and 140 other histologic mimics (20 each epithelioid sarcoma, proliferative fasciitis, nodular fasciitis, cellular benign fibrous histiocytoma, spindle-cell squamous cell carcinoma, spindle-cell rhabdomyosarcoma, and leiomyosarcoma). Immunohistochemistry for FOSB was performed following pressure cooker antigen retrieval using a rabbit monoclonal antibody. Diffuse nuclear immunoreactivity for FOSB (>50% of cells) was observed in 48 of 50 (96%) pseudomyogenic hemangioendotheliomas and 13 of 24 (54%) epithelioid hemangiomas (including all angiolymphoid hyperplasia with eosinophilia type). Both FOSB-negative pseudomyogenic hemangioendothelioma cases were decalcified bone tumors. Only 7 other tumors showed diffuse FOSB expression2 proliferative fasciitis, 2 nodular fasciitis, 1 epithelioid angiosarcoma, 1 spindle-cell angiosarcoma, and 1 epithelioid hemangioendothelioma. Of note, the FOSB-positive epithelioid hemangioendothelioma was negative for CAMTA1 and TFE3. Focal weak FOSB staining was observed in a subset of histologic mimics and is therefore not diagnostically meaningful. In conclusion, FOSB is a highly sensitive and diagnostically useful marker for pseudomyogenic hemangioendothelioma. Immunohistochemistry for FOSB may be helpful to distinguish pseudomyogenic hemangioendothelioma from histologic mimics including epithelioid sarcoma and other vascular neoplasms. As expected, a subset of epithelioid hemangiomas expresses FOSB, including angiolymphoid hyperplasia with eosinophilia. Although occasional cases of nodular and proliferative fasciitis are positive for FOSB, distinction between these tumor types and pseudomyogenic hemangioendothelioma is usually straightforward based on morphology and other immunophenotypic findings.
A distinct subset of round cell sarcomas harbors capicua transcriptional repressor (CIC) rearrangement. Diagnosing these sarcomas can be difficult owing to their resemblance to Ewing sarcoma and ...other 'small round blue cell tumors'; molecular techniques are generally required. Recent gene expression studies of CIC-rearranged sarcomas identified the upregulation of ETV4. We assessed the sensitivity and specificity of ETV4 and WT1 immunohistochemistry for CIC-rearranged sarcoma. We evaluated whole-tissue sections from 40 CIC-rearranged sarcomas, 40 Ewing sarcomas, 4 BCOR-CCNB3 sarcomas, 6 unclassified round cell sarcomas, and 150 histologic mimics. Moderate-to-strong nuclear immunoreactivity for ETV4 in at least 50% of cells was observed in 36 (90%) CIC-rearranged sarcomas and 10 (5%) other tumors, including 5 unclassified round cell sarcomas, 2 Wilms tumors, and 1 each desmoplastic small round cell tumor, melanoma, and small cell carcinoma. Thirty-eight (95%) CIC-rearranged sarcomas showed nuclear staining for WT1, and 34 (85%) were positive for both ETV4 and WT1. Of 182 other tumors evaluated, 34 (19%) showed nuclear WT1 positivity, including all Wilms tumors and desmoplastic small round cell tumors, 5 unclassified round cell sarcomas, and a subset of lymphoblastic lymphomas, rhabdomyosarcomas, mesenchymal chondrosarcomas, carcinomas, and melanomas. In summary, diffuse moderate-to-strong ETV4 expression is present in most CIC-rearranged sarcomas and unclassified round cell sarcomas. More limited expression is seen in small subsets of various other round cell neoplasms. Nuclear WT1 expression is also present in most CIC-rearranged sarcomas and unclassified round cell sarcomas, along with Wilms tumors and desmoplastic small round cell tumors, and subsets of various histologic mimics. The sensitivity and specificity of diffuse ETV4 expression for CIC-rearranged sarcomas are 90% and 95%, respectively, whereas the sensitivity and specificity of WT1 are 95% and 81%, respectively. Diffuse ETV4 along with at least focal WT1 expression is helpful to distinguish CIC-rearranged sarcoma from Ewing sarcoma and other histologic mimics.
Primary mesenchymal tumours of the pleura are uncommon and can be diagnostically challenging due to their overlapping histopathologic and immunophenotypic features. Herein we discuss selected ...mesenchymal tumours of the pleura, including solitary fibrous tumour, calcifying fibrous tumour, desmoid fibromatosis, synovial sarcoma, schwannoma, malignant peripheral nerve sheath tumour, inflammatory myofibroblastic tumour, follicular dendritic cell sarcoma, epithelioid hemangioendothelioma, and desmoplastic small round cell tumour. We review their clinicopathologic characteristics, along with an update on the relevant immunohistochemical and molecular features.
Molecular testing has increasingly been utilized in the evaluation of mesothelioma. Diffuse mesothelioma comprises multiple distinct genetic subgroups. While most diffuse mesotheliomas lack oncogenic ...kinase mutations and instead harbor alterations involving tumor suppressors and chromatin regulators, a minor subset of tumors is characterized by uncommon alterations such as germline mutations, genomic near-haploidization, ALK rearrangement, ATF1 rearrangement, or EWSR1::YY1 fusion.
To provide updates on the salient molecular features of diffuse mesothelioma, mesothelioma in situ, and other mesothelial lesions: well-differentiated papillary mesothelial tumor, adenomatoid tumor, peritoneal inclusion cyst, and others. We consider the diagnostic, prognostic, and predictive utility of molecular testing in mesothelial lesions.
We performed a literature review of recently described genetic features, molecular approaches, and immunohistochemical tools, including BAP1, MTAP, and merlin in mesothelioma and other mesothelial lesions.
Our evolving understanding of the molecular diversity of diffuse mesothelioma and other mesothelial lesions has led to considerable changes in pathology diagnostic practice, including the application of immunohistochemical markers such as BAP1, MTAP, and merlin (NF2), which are surrogates of mutation status. In young patients and/or those without significant asbestos exposure, unusual mesothelioma genetics such as germline mutations, ALK rearrangement, and ATF1 rearrangement should be considered.
Malignant peritoneal mesothelioma is a rare aggressive tumor that arises from the peritoneal lining. While recurrent BAP1 mutations have been identified in a subset of mesotheliomas, molecular ...characteristics of peritoneal mesotheliomas, including those lacking BAP1 alterations, remain poorly understood. Using targeted next-generation sequencing, we examined the molecular features of 26 diffuse malignant peritoneal mesotheliomas. As part of an exploratory analysis, we analyzed an additional localized peritoneal mesothelioma and one well-differentiated papillary mesothelioma with invasive foci. Genomic characterization identified categories of diffuse malignant peritoneal mesotheliomas: The first group included 18 (69%) tumors with recurrent BAP1 alterations, with eight (31%) having more than one BAP1 alterations, and concomitant alterations in PBRM1 (46%) and SETD2 (35%). All tumors with complete loss of BAP1 expression by immunohistochemistry harbored BAP1 molecular alterations. PBRM1 alterations were significantly enriched in the BAP1-altered cohort. Frequent copy number loss of BAP1, ARID1B, PRDM1, PBRM1, SETD2, NF2, and CDKN2A was noted. The second group included eight (31%) BAP1-wild-type tumors: two with TP53 mutations, one with a TRAF7 activating mutation, one with a SUZ12 inactivating mutation, and three with ALK rearrangements that we previously published. One TP53-mutant biphasic mesothelioma showed evidence of genomic near-haploidization showing loss of heterozygosity of all chromosomes except 5, 7, 16, and 20. The localized peritoneal mesothelioma harbored a nonsense CHEK2 mutation, and the well-differentiated papillary mesothelioma with invasive foci harbored no reportable variants. In conclusion, we described the genetic categories of diffuse malignant peritoneal mesotheliomas, with BAP1-mutant and BAP1-wild-type groups. Our findings implicated DNA repair, epigenetics, and cell cycle regulation in the pathogenesis of peritoneal mesotheliomas, with identification of potential therapeutic targets.
Aims
Infantile fibrosarcoma is characterised by intersecting fascicles of spindle cells and ETV6–NTRK3 gene fusion in most cases. Given histological overlap with other spindle‐cell tumours, the ...diagnosis can be challenging and often requires molecular confirmation. A recently developed pan‐TRK antibody shows promise for identifying tumours with NTRK fusions. The purpose of this study was to evaluate the potential diagnostic utility of pan‐TRK immunohistochemistry for infantile fibrosarcoma.
Methods and results
We evaluated whole‐tissue sections from 210 cases, including 15 infantile fibrosarcomas; five each lipofibromatosis‐like neural tumour and lipofibromatosis; 10 each primitive myxoid mesenchymal tumour of infancy (PMMTI) and low‐grade myofibroblastic sarcoma; 15 each fibrous hamartoma of infancy (FHI), myofibroma/myofibromatosis and desmoid‐type fibromatosis; and 20 each low‐grade fibromyxoid sarcoma, synovial sarcoma, spindle‐cell rhabdomyosarcoma, malignant peripheral nerve sheath tumour, fibrosarcomatous dermatofibrosarcoma protuberans (F‐DFSP) and nodular fasciitis. Immunohistochemistry was performed using a rabbit monoclonal pan‐TRK antibody. Immunoreactivity for pan‐TRK was observed in all 15 (100%) infantile fibrosarcomas, including diffuse immunoreactivity (>50% of cells) in 14 (93%) cases. Pan‐TRK was positive in all five (100%) lipofibromatosis‐like neural tumours. Of the 190 histological mimics, diffuse pan‐TRK immunoreactivity was noted in 16 (8%) cases, including five PMMTI, five FHI (highlighting predominantly the primitive myxoid spindle‐cell components), three F‐DFSP, one low‐grade myofibroblastic sarcoma, one myofibroma and one spindle‐cell rhabdomyosarcoma.
Conclusions
Diffuse pan‐TRK immunoreactivity is a highly sensitive but not entirely specific diagnostic marker for infantile fibrosarcoma, and may be helpful in selecting patients for TRK‐targeted therapy. As expected, lipofibromatosis‐like neural tumours, which harbour NTRK1 fusions, also show diffuse pan‐TRK immunoreactivity.
Ewing sarcoma shows considerable histologic overlap with other round cell tumors. NKX2-2, a homeodomain transcription factor involved in neuroendocrine/glial differentiation and a downstream target ...of EWSR1-FLI1, has been reported as an immunohistochemical marker for Ewing sarcoma. We assessed the specificity of NKX2-2 for Ewing sarcoma compared with other round cell malignant neoplasms and other soft tissue tumors with EWSR1 translocations. We evaluated whole-tissue sections from 270 cases: 40 Ewing sarcomas (4 with atypical/large cell features), 20 CIC-DUX4 sarcomas, 5 BCOR-CCNB3 sarcomas, 9 unclassified round cell sarcomas, 10 poorly differentiated synovial sarcomas, 10 lymphoblastic lymphomas, 10 alveolar rhabdomyosarcomas, 10 embryonal rhabdomyosarcomas, 10 Merkel cell carcinomas, 10 small cell carcinomas, 20 melanomas, 5 NUT midline carcinomas, 10 Wilms tumors, 10 neuroblastomas, 10 olfactory neuroblastomas, 12 mesenchymal chondrosarcomas, 10 angiomatoid fibrous histiocytomas, 10 clear cell sarcomas, 5 gastrointestinal clear cell sarcoma-like tumors, 5 desmoplastic small round cell tumors, 10 extraskeletal myxoid chondrosarcomas, 10 soft tissue and cutaneous myoepitheliomas, and 19 myoepithelial carcinomas. NKX2-2 positivity was defined as moderate-to-strong nuclear immunoreactivity in at least 5% of cells. NKX2-2 was positive in 37/40 (93%) Ewing sarcomas, including all atypical Ewing sarcomas and cases with known EWSR1-FLI1 or EWSR1-ERG fusion; 85% of Ewing sarcomas showed diffuse (>50%) staining. NKX2-2 was positive in 9 (75%) mesenchymal chondrosarcomas, 8 (80%) olfactory neuroblastomas, 1 CIC-DUX4 sarcoma, 1 poorly differentiated synovial sarcoma, 1 neuroblastoma, 2 unclassified round cell sarcomas, and 3 small cell carcinomas; all other EWSR1-associated tumors were negative for NKX2-2, apart from 1 desmoplastic small round cell tumor, 1 myoepithelioma, and 1 myoepithelial carcinoma. In summary, NKX2-2 is a sensitive but imperfectly specific marker for Ewing sarcoma. Nonetheless, NKX2-2 may be helpful to distinguish Ewing sarcoma from some histologic mimics including CIC-DUX4 and BCOR-CCNB3 sarcomas. Most other EWSR1-associated soft tissue tumors are negative for NKX2-2.
A diverse group of both benign and malignant spindle cell tumors can involve the pleura or the peritoneum. Due to their rarity and overlapping morphologic features, these tumors can pose considerable ...diagnostic difficulty in surgical pathology. As these tumors differ in their prognosis and clinical management, their correct pathologic diagnosis is critical. In addition to histologic assessment, select immunohistochemical and molecular tools can aid the distinction among these tumors. In this review, we consider some of the major histologic differential diagnosis of spindle cell tumors involving these serosal membranes. This list of tumors includes solitary fibrous tumor, inflammatory myofibroblastic tumor, desmoid fibromatosis, synovial sarcoma, sarcomatoid carcinoma, spindle cell melanoma, dedifferentiated liposarcoma, epithelioid hemangioendothelioma, and sarcomatoid mesothelioma. We describe their salient clinicopathologic and genetic findings, with a review on some of the recent discoveries on their molecular pathogenesis.
Small-cell lung cancer (SCLC) is an aggressive malignancy in which inhibitors of PARP have modest single-agent activity. We performed a phase I/II trial of combination olaparib tablets and ...temozolomide (OT) in patients with previously treated SCLC. We established a recommended phase II dose of olaparib 200 mg orally twice daily with temozolomide 75 mg/m
daily, both on days 1 to 7 of a 21-day cycle, and expanded to a total of 50 patients. The confirmed overall response rate was 41.7% (20/48 evaluable); median progression-free survival was 4.2 months 95% confidence interval (CI), 2.8-5.7; and median overall survival was 8.5 months (95% CI, 5.1-11.3). Patient-derived xenografts (PDX) from trial patients recapitulated clinical OT responses, enabling a 32-PDX coclinical trial. This revealed a correlation between low basal expression of inflammatory-response genes and cross-resistance to both OT and standard first-line chemotherapy (etoposide/platinum). These results demonstrate a promising new therapeutic strategy in SCLC and uncover a molecular signature of those tumors most likely to respond. SIGNIFICANCE: We demonstrate substantial clinical activity of combination olaparib/temozolomide in relapsed SCLC, revealing a promising new therapeutic strategy for this highly recalcitrant malignancy. Through an integrated coclinical trial in PDXs, we then identify a molecular signature predictive of response to OT, and describe the common molecular features of cross-resistant SCLC.
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