Co‐existence of multiple myeloma and perivascular endothelial cell tumor

A 56-year-old woman presented with a left upper thigh mass and associated leg weakness. On work-up, she was found to be anemic (hemoglobin 51 g/L) with hypercalcemia (3.49 mmol/L), serum free light chain spike, Bence Jones protein, and a compression fracture of L2. A peripheral blood smear showed rouleaux and rare circulating plasma cells. A bone marrow aspirate was hemodilute but contained many plasma cells (Panel A). A bone marrow biopsy (B) showed 80% plasma cells which were stained positive for CD138 (C), kappa (D), CD56, and negative for lambda (E). This was consistent with a diagnosis of multiple myeloma (MM). Molecular cytogenetic studies were negative for high-risk myeloma genetic abnormalities. Clinically, the leg mass was initially thought to represent an extramedullary manifestation of MM. However, a biopsy of the leg mass showed a high-grade malignant pleomorphic tumor comprising polygonal cells with large irregular nuclei, fine chromatin, prominent nucleoli, and abundant eosinophilic cytoplasm (F). The tumor cells were positive for TFE3 (G) and MIFT (H) with focal positivity for SMA (I), S100, and Melan-A/HMB45 cocktail, negative for CD138. A diagnosis of malignant perivascular endothelial cell tumor (PEComa) was made (Figure 1). Although patients with MM and coexisting with a different primary neoplasm (either hematological or solid organ neoplasm) have previously been described,1 to our knowledge, this is the first report of concurrent MM and PEComa. PEComas are a distinctive mesenchymal neoplasm arising from perivascular epithelioid cells that usually demonstrate combined myomelanocytic immunophenotype. Most PEComas are sporadic, however, and can be associated with tuberous sclerosis complex harboring deletions of TSC2 gene with the activation of mTOR pathway.2 Co-existence of MM with solid tumors seems to appear sporadically, whereby genetic predisposition, tumor-induced immunodeficiency, deregulated release of cytokines, and chronic inflammation may contribute to such associations.1 It is unclear whether these two neoplasms were linked as no further molecular testing was performed in this case. This case also highlights an important clinical consideration that unrelated solid tumors can co-exist in the setting of MM that might mimic extramedullary disease. The authors have no competing interests.

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