Soft tissue sarcomas are a rare group of mesenchymal malignancies that account for just 1% of all cancers. However, although rare, they account for a disproportionate share of mortality in young adults.
We came across a man in his 50s, who was diagnosed with stage 4 (metastatic) leiomyosarcoma arising from the anterior abdominal wall. Initial treatment with palliative cytotoxic chemotherapy was futile, and the sarcoma continued to progress through. Molecular profiling revealed a MSH6 R922* truncating mutation. The tumor mutational burden was 11.35 mutations/Mb, and microsatellite instability (MSI) status was reported as MSI-high. Through further research studies, we observed that the tumor has a mild to moderate infiltrate of lymphocytes and plasma cells, especially at the tumor-stroma interface.
The patient was then treated with an immune checkpoint inhibitor, which resulted in a rapid reduction in tumor size, necrosis and liquefaction requiring surgery. Histologic examination of the resected tumor showed extensive necrosis with no residual viable tumor, in keeping with pathologic complete response - the patient remains disease-free beyond 1 year on.
Multiplex immunofluorescence showing various tumor-infiltrating immune cells (source: Tay et al. JCO Precis Oncol. 2022)
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