Logan, Suzanna

AbstractCollision 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.

Abstract The CD8 + T-cell response is prognostic for survival outcomes in several tumor types. However, whether this extends to tumors in the brain, an organ with barriers to T cell entry, remains unclear. Here, we analyzed immune infiltration in 67 brain metastasis (BrM) and found high frequencies of PD1 + TCF1 + stem-like CD8 + T-cells and TCF1- effector-like cells. Importantly, the stem-like cells aggregate with antigen presenting cells in immune niches, and niches were prognostic for local disease control. Standard of care for BrM is resection followed by stereotactic radiosurgery (SRS), so to determine SRS’s impact on the BrM immune response, we examined 76 BrM treated with pre-operative SRS (pSRS). pSRS acutely reduced CD8 + T cells at 3 days. However, CD8 + T cells rebounded by day 6, driven by increased frequency of effector-like cells. This suggests that the immune response in BrM can be regenerated rapidly, likely by the local TCF1 + stem-like population.

AbstractTumor‐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.