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We report on a morphologic variant of multiple myeloma, identified in a 39-year-old man, with osteolytic lesions in two ribs and three lumbar vertebrae. Serum electrophoresis was normal and immunofixation of serum and urine was negative. Histologic examination of a resected rib revealed a homogeneous population of neoplastic plasma cells with granular and eosinophilic cytoplasm. Immunohistochemical stains showed monoclonality for λ light chain and negativity for all heavy chains. At the ultrastructural level, the cytoplasm of the neoplastic plasma cells was almost totally occupied by round and elongated mitochondria, pushing the rough endoplasmic reticulum to the periphery. To the best of our knowledge, only two similar cases have been reported in the literature so far. The usefulness of obtaining a clinicopathologic correlation for the behaviour of this extremely rare variant of multiple myeloma is discussed.

The 4th case of plasma cell neoplasm associated with a hypereosinophilic syndrome is described and compared with the previous reports. Hypereosinophilia in the present patient displayed some borderline traits with eosinophilic leukemia. Myeloproliferative disorders of the eosinophilic line often present as a precancerous state, but sometimes they seem to acquire malignant independence. In our patient the occurrence of a plasmocytoma with a dramatic course leads to suspect an underlying complex genetic aberration.