Spindle Cell Sarcoma

EPS15/EPS15L1::KLF17-rearranged sarcoma has distinctive histologic findings, including diffuse MUC4 expression. Recognition is clinically important given its potential for late recurrence and metastasis.

This finding broadens the known immunophenotypic spectrum of MUC4-positive fibroblastoma and challenges current assumptions regarding β‑catenin localization in APC-altered soft tissue tumors. Additional clinical, radiologic, and long-term follow-up data may help refine our understanding of the biological behavior and diagnostic boundaries of this emerging entity.

The mass showed significantly increased FDG uptake. The patient underwent surgical resection, and histopathologic examination revealed a spindle cell tumor positive for CD21 and CD35, confirming the diagnosis of FDCS.

This review aims to highlight the key clinicopathologic features of these tumors to facilitate accurate diagnosis, discuss ancillary studies that assist in navigating the differential diagnoses, and outline strategies to avoid common diagnostic pitfalls. Finally, we emphasize when molecular characterization may be necessary to guide diagnosis and support appropriate clinical management.

NTRK3 gene fusions occur in a subset of plaque-like CD34-positive dermal fibromas, providing additional molecular insight into this rare superficial spindle cell lesion. Together with emerging literature, these findings support a role for recurrent kinase gene rearrangements in a subset of CD34-positive plaque-like superficial spindle cell tumours, while underscoring the continued importance of clinicopathologic correlation in defining this evolving spectrum.

Immunohistochemistry showed diffuse nuclear STAT6 and CD34 positivity, and molecular analysis confirmed a NAB2:::STAT6 fusion. This case highlights the diagnostic pitfalls associated with myxoid change in vulvar mesenchymal tumors and underscores the importance of immunohistochemical and molecular confirmation.

This case contributes additional data to the limited literature on tumors with SMARCA2::CREM fusions. It highlights the potential utility of comprehensive molecular testing, including broader fusion panels or whole-transcriptome sequencing, in the evaluation of diagnostically challenging uterine neoplasms.

To our knowledge, this is the first report of Mesocestoides spp. parasitism associated with a soft tissue sarcoma in a dog.

P1, N=14, Active, not recruiting, Jonsson Comprehensive Cancer Center | Trial completion date: Jan 2027 --> Jan 2028 | Trial primary completion date: Jan 2026 --> Jan 2027

Immunohistochemistry confirmed the diagnosis with diffuse cytoplasmic CD34 and strong nuclear Signal Transducer and Activator of Transcription 6 (STAT6) expression. No significant mitotic activity or necrosis was identified.

Therefore, owing to overlapping IHC profiles, definitive diagnosis of PRSS warrants SS18::SSX gene molecular testing to avoid misclassification, especially given the therapeutic and prognostic implications. Integration of morphology, IHC, and molecular studies remains paramount for accurate diagnosis of such rare renal spindle cell neoplasms.

Therefore, MTAP IHC can be useful in evaluating spindle cell lesions of the urinary tract, as loss is significantly more common in SarUC than in IMT, and enriched in the mesenchymal component of biphasic SarUC. However, MTAP loss can be seen in both entities, and the diagnosis of IMT-like spindle cell tumors in the urinary tract requires careful integration of morphologic, immunohistochemical, and molecular data.