Frequent CD30 Expression in an Emerging Group of Mesenchymal Tumors With NTRK, BRAF, RAF1, or RET Fusions

Primary cutaneous rhabdomyosarcoma with EWSR1/FUS::TFCP2 fusion: four new cases with distinctive morphology, immunophenotypic, and genetic profile

EWSR1/FUS::TFCP2-rearranged rhabdomyosarcoma (RMS) is a rare tumor with an aggressive clinical course, a predilection for craniofacial bones, spindled and/or epithelioid histomorphology, and positive immunohistochemistry (IHC) for epithelial and myogenic markers, along with variable ALK expression. Herein, we present four additional cases of primary cutaneous TFCP2-rearranged RMS. Notably, one tumor (case 1) displayed a varied pathological spectrum, initially presenting as a low-grade spindle cell neoplasm, but progressed into a high-grade spindle/epithelioid tumor. Another case (case 2) exhibited a predominant high-grade epithelioid/rhabdoid morphology. The third case (case 3) demonstrated a biphasic appearance of spindle and epithelioid cell proliferation, presenting with a low-grade morphology, and the last case (case 4) showed a predominant epithelioid morphology. All cases showed myogenic differentiation associated with keratins and ALK immunoreactivity. Interestingly, the two cases with high-grade and epithelioid morphology demonstrated CD30 immunoexpression. RNAseq or FISH revealed EWSR1 or FUS::TFCP2 gene fusion, and two cases with aggressive evolution showed ALK cluster-amplification as well, a finding that has not been previously reported. Two cases displayed aggressive behavior, with case 1 experiencing local recurrences and undergoing transformation into a high-grade epithelioid tumor, whereas case 2 initially presented as an epithelioid high-grade neoplasm, subsequently developing lymph node metastases and shortly thereafter distant metastases. In contrast, patients 3 and 4 are alive with no evidence of disease. The distinctive morphology and immunoprofile of this neoplasm may pose challenges in the differential diagnosis with cutaneous neoplasms showing keratins, ALK, and CD30 immunoreactivity. Nonetheless, ALK and CD30 overexpression may offer avenues for targeted therapy.

Soft tissue tumor with BRAF and NRAS mutations sharing features with NTRK-rearranged spindle cell neoplasm: A case report expanding the spectrum of spindle cell tumor with kinase gene alterations

NTRK-rearranged spindle cell neoplasm is a group of tumors characterized by NTRK1/2/3 gene fusion. Recently, tumors with other kinase fusion genes were reported to exhibit similar morphologies. Herein, we discuss an adult-onset soft tissue tumor with similar histologic patterns as kinase gene fusion-related tumors but with BRAF and NRAS mutations. A female in her 40s had a 40 mm tumor with an unclear border in the soft tissue of her foot joint. Short spindle-shaped tumor cell proliferation with abundant capillaries and collagen fiber bundles were observed. The tumor infiltrated the subcutaneous adipose tissue, exhibiting a lipofibromatosis-like pattern. Immunohistochemically, the tumor cells coexpressed CD34, S-100, and BRAF V600E. Whole-exome sequencing revealed BRAF p.V600E and NRAS p.Q61K mutations. Since BRAF activation occurs in BRAF fusion gene tumors and BRAF mutations, they could share a similar mechanism in tumorigenesis. This case suggests the further expansion of kinase-related spindle cell tumors.

Extra-abdominal and intra-abdominal FET::CREM fusion mesenchymal neoplasms: comparative clinicopathological study of 9 new cases further supporting a distinct potentially aggressive sarcoma and report of novel sites

With the wide use of RNA sequencing technologies, the family of FET::CREB fusion mesenchymal neoplasms has expanded rapidly to include potentially aggressive neoplasms, not fitting any well established WHO entity. Recently, a group of intra-abdominal FET(EWSR1/FUS)::CREB(CREM/ATF1) fused unclassified neoplasms has been reported followed by recent recognition of an analogous extra-abdominal category of unclassified neoplasms carrying EWSR1::ATF1 fusions. We describe 9 additional tumors (5 extra-abdominal and 4 abdominal) carrying an EWSR1::CREM (n = 8) and FUS::CREM (n = 1) fusion. Patients were 7 females and 2 males aged 10 to 75 years (median, 34). Extra-abdominal tumors originated in the head and neck (2 sinonasal, 1 orbital) and soft tissues (1 gluteal, 1 inguinal). Abdominal tumors involved stomach (2), mesentery (1), and kidney (1). Tumor size ranged from 3.5 to 11 cm (median, 6). Treatment was radical surgery with (5) or without (2) neo/adjuvant radio/chemotherapy. Extended follow-up of 5 patients (21-52 months; median, 24) showed an aggressive course in two (40%); one died of disseminated metastases 52 months after several intensified chemotherapy regimens, and one was alive with progressive abdominal disease at 21 months. The immunophenotype of the two subcohorts was significantly overlapping with variable expression of EMA (7 of 8), keratin AE1/AE3 (5 of 9), CD99 (4 of 7), MUC4 (2 of 8), ALK (3 of 8), synaptophysin (3 of 9), chromogranin (1 of 8), CD34 (3 of 6), CD30 (1 of 6), PAX8 (1 of 7), and inhibin (1 of 7), but no reactivity with desmin (0 of 8), S100 (0 of 8), and SOX10 (0 of 8). This series further solidifies the notion that FET::CREB fusions are not limited to the triad of angiomatoid fibrous histiocytoma, clear cell sarcoma, and malignant gastrointestinal neuroectodermal tumor, but characterize an emerging family of potentially aggressive neoplasms occurring at both intra- and extra-abdominal sites. These tumors underscore the promiscuity of the FET::CREB fusions and highlight the pivotal role of phenotype-oriented classification of these neoplasms that share the same genotype, still featuring significant biological and behavioral distinctness.

Update on cutaneous mesenchymal tumors in the 5th edition of WHO classification of skin tumors with an emphasis on new fusion-associated neoplasms

The section on mesenchymal tumors in the 5th edition of WHO classification of skin tumors has undergone several changes, the most important of which is the inclusion of newly identified tumor entities, which will be the main focus of this review article. These specifically include three novel cutaneous mesenchymal tumors with melanocytic differentiation, and rearrangements of the CRTC1::TRIM11, ACTIN::MITF, and MITF::CREM genes as well as EWSR1::SMAD3-rearranged fibroblastic tumors, superficial CD34-positive fibroblastic tumors, and NTRK-rearranged spindle cell neoplasms. Some of the other most important changes will be briefly mentioned as well.

[Molecular testing in mesenchymal neoplasms: What, when, and how to test? : A review with a special focus on the value of next-generation immunochemistry as a substitute for molecular testing]

With the widespread use of diverse modern molecular testing tools, the last two decades have seen significant advances in the classification of soft tissue neoplasms. Specifically, numerous molecularly defined new entities have been introduced and many established older entities have received more insightful molecular studies that have developed their classification further. The discrepant therapeutic and prognostic implications of this evolving complexity of the nosology of neoplastic diseases make the precise subtyping of soft tissue neoplasms unavoidable. However, these rapid developments of the modern diagnostic molecular pathology did not only offer efficient solutions to many complex classification issues, but they were accompanied by similarly complex and diverse emerging problems. Most importantly, these advances have not only challenged the historical dogma of some phenotypes that were once considered specific, but they also have questioned the value of diagnostic immunohistochemistry compared to emerging modern diagnostic molecular tools. Moreover, the central question of when to test, what to test, and how to test became more confusing. This review addresses the major molecular categories in soft tissue neoplasms, their characteristics, and the criteria to be used for selecting the most appropriate molecular diagnostic tool to be used in individual cases with a special focus on the value of next generation immunohistochemistry as a substitute for molecular testing.

S100 and CD34 positive spindle cell tumors of the uterine cervix with EGFR mutation: a hitherto unrecognized neoplasm phenotypically and epigenetically overlapping with "NTRK-rearranged spindle cell neoplasms" of the uterus

NTRK-rearranged spindle cell neoplasm represents an emerging entity included in the latest 5th edition of WHO classification of both soft tissue and female genital tumors. By immunohistochemistry, they are commonly positive for CD34, S100 protein, and CD30 and typically harbor fusions of kinase genes such as NTRK1/2/3, RET, and BRAF. In the gynecological tract, they typically affect the uterine cervix or uterine body. Most of the reported cases had fibrosarcoma-like morphology, occasionally showing perivascular and stromal hyalinization with only a few cases showing a less cellular spindle cell proliferation. Except for one case with RET fusion, all other gynecological cases harbored exclusively NTRK1/2/3 fusions. Besides kinase gene fusions, the analogous tumors in soft tissues may also harbor activating EGFR or BRAF point mutations, but no such case has been described in the uterus. Herein we are reporting two cases from the uterine cervix showing morphology and molecular features previously unreported at this anatomic site. The patients were 46 and 34 years old and clinically presented with unremarkable cervical polyps each measuring 8 mm in diameter. Histologically, both cases had a rounded polypoid outline and were composed of hypocellular proliferation of bland spindle cells lacking mitotic activity and growing in a fibrotic stroma which was punctuated by prominent small vessels with thick hyalinized walls. Immunohistochemically, both showed a diffuse expression of CD34, CD30, and S100 protein, whereas SOX10 was negative. Both cases harbored exon 20 EGFR mutation and did not reveal any fusions or significant copy number changes. The patient in case 1 was treated by hysterectomy with salpingectomy with no other residual tumor detected, and she was alive and well 27 months after the diagnosis. The patient in case 2 had no other known tumors at the time of diagnosis, but no follow-up is available. We believe the reported cases represent a hitherto unrecognized variant of "NTRK-rearranged spindle cell neoplasms" of the uterine cervix with novel EGFR mutations.

An unusual presentation of dermatofibrosarcoma protuberans: A case of fibrosarcomatous dermatofibrosarcoma protuberans with pleomorphic angiectatic tumor-like changes

Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive superficial mesenchymal neoplasm characterized by monomorphic spindle-cell proliferation with a storiform pattern. It can demonstrate pigmentation, myxoid changes, myoid differentiation, plaque-like growth, and fibrosarcomatous features; its varied presentation often complicates diagnosis. We report an extremely rare case of fibrosarcomatous DFSP with features reminiscent of a pleomorphic hyalinizing angiectatic tumor (PHAT) in a 73-year-old male. The diagnosis was confirmed using a reverse transcription polymerase chain reaction. To the best of our knowledge, PHAT-like changes in DFPS have not been described so far. Therefore, this report provides a novel variant of DFSP and expands the differential diagnosis of DFSP and PHAT.

Myxoid Inflammatory Myofibroblastic Sarcoma: Clinicopathologic Analysis of 25 Cases of a Distinctive Sarcoma With Deceptively Bland Morphology and Aggressive Clinical Behavior

The number of recognized sarcoma types harboring targetable molecular alterations continues to increase. Here we present 25 examples of a distinctive myofibroblastic tumor, provisionally termed "myxoid inflammatory myofibroblastic sarcoma," which might be related to inflammatory myofibroblastic tumor, and which occurred in 13 males (52%) and 12 females at a median age of 37 years (range: 7 to 79 years). Primary tumor sites were peritoneum (18 patients; 72%), paratesticular (2; 8%), chest wall (1), upper extremity (1), esophagus (1), retroperitoneum (1), and uterus (1). Nine peritoneal tumors (50%) were multifocal at presentation; all other tumors were unifocal. Tumors showed bland-to-mildly-atypical neoplastic myofibroblasts in a myxoid stroma, with prominent inflammatory infiltrates in 22 cases (88%). Most tumors showed delicate branching stromal vessels like those of myxoid liposarcoma, and most showed infiltrative growth through non-neoplastic tissue. Immunohistochemistry demonstrated expression of SMA (19/25 tumors; 76%), desmin (13/22; 59%), and CD30 (5/11; 45%), while ALK was expressed in 1 tumor (of 25; 4%) that was negative for ALK rearrangement. Sequencing of 11 tumors showed seven to harbor tyrosine kinase fusions (4 PDGFRB , 2 PML :: JAK1 , 1 SEC31A :: PDGFRA ). Two instead harbored hot spot KRAS mutations (G12V and Q61H), and 2 were negative for known driving alterations. Clinical follow-up was available for 18 patients (72%; median: 2.7 years; range: 4 mo-12.3 years). Nine patients (50%) were alive with no evidence of disease, 5 (28%) died of disease, and 4 (22%) were alive with disease. Seven patients (39%) experienced peritoneal relapse or distant metastasis. Two patients showed disease progression on conventional, nontargeted chemotherapy. The patient whose tumor harbored SEC31A :: PDGFRA was treated after multiple relapses with imatinib and sunitinib therapy, with progression-free periods of 5 and 2 years, respectively. Despite its bland appearance, myxoid inflammatory myofibroblastic sarcoma harbors a significant risk for disseminated disease, particularly when it occurs in the peritoneum. Targeted therapy could be considered for patients with disseminated disease.

RAF1 gene fusions are recurrent driver events in infantile fibrosarcoma-like mesenchymal tumors

Infantile fibrosarcomas (IFS) and congenital mesoblastic nephroma (CMN) are rare myofibroblastic tumors of infancy and early childhood commonly harboring the ETV6::NTRK3 gene fusion. IFS/CMN are considered as tumors with an 'intermediate prognosis' as they are locally aggressive, but rarely metastasize, and generally have a favorable outcome. A fraction of IFS/CMN-related neoplasms are negative for the ETV6::NTRK3 gene rearrangement and are characterized by other chimeric proteins promoting MAPK signaling upregulation. In a large proportion of these tumors, which are classified as IFS-like mesenchymal neoplasms, the contributing molecular events remain to be identified. Here, we report three distinct rearrangements involving RAF1 among eight ETV6::NTRK3 gene fusion-negative tumors with an original histological diagnosis of IFS/CMN. The three fusion proteins retain the entire catalytic domain of the kinase. Two chimeric products, GOLGA4::RAF1 and LRRFIP2::RAF1, had previously been reported as driver events in different cancers, whereas the third, CLIP1::RAF1, represents a novel fusion protein. We demonstrate that CLIP1::RAF1 acts as a bona fide oncoprotein promoting cell proliferation and migration through constitutive upregulation of MAPK signaling. We show that the CLIP1::RAF1 hyperactive behavior does not require RAS activation and is mediated by constitutive 14-3-3 protein-independent dimerization of the chimeric protein. As previously reported for the ETV6::NTRK3 fusion protein, CLIP1::RAF1 similarly upregulates PI3K-AKT signaling. Our findings document that RAF1 gene rearrangements represent a recurrent event in ETV6::NTRK3-negative IFS/CMN and provide a rationale for the use of inhibitors directed to suppress MAPK and PI3K-AKT signaling in these cancers. © 2024 The Pathological Society of Great Britain and Ireland.

Abdominal inflammatory myofibroblastic tumour: Clinicopathological and molecular analysis of 20 cases, highlighting potential therapeutic targets

AIMS

Inflammatory myofibroblastic tumour (IMT) is a rare mesenchymal neoplasm of intermediate malignant potential, occurring at any age and at multiple sites. Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is an aggressive subtype of IMT, typically involving the abdomen. Most IMTs harbour kinase gene fusions, especially involving ALK and ROS1, but 20-30% of IMTs show no detectable translocations. The aim of this study is to further delineate clinicopathological and molecular characteristics of abdominal IMT and discover potential new therapeutic targets.

METHODS AND RESULTS

In 20 IMTs, including four EIMS, RNA fusion analysis was performed, followed by multiplex DNA analysis if no ALK or ROS1 fusion was detected. Fourteen IMTs (70.0%) had an ALK translocation and the fusion partner was identified in 11, including a RRBP1::ALK fusion, not previously described in classical (non-EIMS) IMT. RANBP2::ALK fusion was demonstrated in all EIMS. One IMT had a ROS1 fusion. In all ALK/ROS1 translocation-negative IMTs mutations or fusions - as yet unreported in primary IMT - were found in genes related to the receptor tyrosine kinase (RTK)/PI3K/AKT pathway. Three of four patients with EIMS died of disease [mean survival 8 months (4-15 months)], whereas only one of 14 classical IMT patients succumbed to disease [mean follow-up time 52 months (2-204 months); P < 0.01].

CONCLUSION

This study shows the wide clinical spectrum of abdominal IMTs and affirms the poor prognosis of EIMS, raising discussion about its status as IMT subtype. Furthermore, the newly detected alterations of the RTK/PI3K/AKT pathway expand the molecular landscape of IMTs and provide potential therapeutic targets.

NTRK Therapy among Different Types of Cancers, Review and Future Perspectives

Neurotrophic tyrosine receptor kinase (NTRK) has been a remarkable therapeutic target for treating different malignancies, playing an essential role in oncogenic signaling pathways. Groundbreaking trials like NAVIGATE led to the approval of NTRK inhibitors by the Food and Drug Administration (FDA) to treat different malignancies, significantly impacting current oncology treatment. Accurate detection of NTRK gene fusion becomes very important for possible targeted therapy. Various methods to detect NTRK gene fusion have been applied widely based on sensitivity, specificity, and accessibility. The utility of different tests in clinical practice is discussed in this study by providing insights into their effectiveness in targeting patients who may benefit from therapy. Widespread use of NTRK inhibitors in different malignancies could remain limited due to resistance mechanisms that cause challenges to medication efficacy in addition to common side effects of the medications. This review provides a succinct overview of the application of NTRK inhibitors in various types of cancer by emphasizing the critical clinical significance of NTRK fusion gene detection. The discussion also provides a solid foundation for understanding the current challenges and potential changes for improving the efficacy of NTRK inhibitor therapy to treat different malignancies.

Spindle Cell Tumors of the Sinonasal Tract: A Diagnostic Update with Focus on Ancillary Workup

Spindle cell neoplasms arising in the head and neck may be challenging to recognize due to their relative rarity. While underlying molecular alterations are increasingly elucidated, testing for these features may not be readily available. In most cases, combinations of key morphologic features and diagnostic immunohistochemical markers can be used to replace molecular diagnostics. Conversely, some molecular alterations and expression of their surrogate biomarkers are not specific for any one entity, and it is important to recognize these to avoid diagnostic pitfalls. In this review, we discuss both old and new spindle cell tumors of the sinonasal tract, with an emphasis on histologic features and clinically relevant immunohistochemical markers serving as surrogate markers for underlying genomic alterations.

CD30 expression in an emerging group of mesenchymal spindle cell neoplasms with ALK fusion detected by flow cytometry and immunohistochemistry

An emerging group of spindle cell neoplasms harboring fusions involving NTRK or non-NTRK kinase genes often share characteristic S100 and/or CD34 expression; however, the diagnostic utility of immunohistochemical stains is not well established in this family owing to their lack of specificity. Recently, CD30 expression in spindle cell neoplasms with kinase gene fusions, such as NTRK, BRAF, RAF1, and RET, has been increasingly identified. We herein report a 10-year-old girl with high-grade spindle cell sarcoma of the neck. Prior to histopathological evaluation, flow cytometry (FCM) analysis and touch smear cytology of the tumor tissue revealed CD34+ and dimCD30+ spindle cell populations. Histopathologically, the case was characterized by monomorphic spindle-shaped cytomorphology with CD30, S100, and CD34 positivity and harbored close similarities with spindle cell neoplasms with NTRK or non-NTRK gene fusions. Subsequently, a comprehensive next-generation sequencing sarcoma panel identified a rare PLEKHH2::ALK fusion, and a diagnosis of ALK-rearranged spindle cell neoplasm was made. The patient showed significant tumor response to single-agent treatment with alectinib, an ALK-tyrosine kinase inhibitor. This case supports that CD30 is expressed in an ALK-rearranged mesenchymal neoplasm. The benefit of the early detection of CD30 expression by FCM for a prompt diagnosis and treatment is highlighted in the context of an aggressive clinical course. This case represents a learning experience regarding the need to the check the status of CD30 expression in these tumors and suggests the potential clinical benefits of CD30-targeted therapy.