High-grade plasmablastic neoplasm of humerus in an HIV-negative patient, which was indeterminate between plasmablastic lymphoma and plasmablastic myeloma

Plasmablastic lymphoma (PBL) of bone is a rare neoplasm that shares many confusing cytomorphological and immunohistochemical features with plasmablastic plasma cell myeloma (PBPCM). A 47-year-old female patient presented with a bony swelling and bone pain in the left humerus for the last 6 months. On radiological examination (x-ray and computed tomography) it appeared to be a lytic lesion, and a pathological fracture was detected. The patient was HIV-negative. Fine needle aspiration (FNA) was done from the lesion, which was inconclusive. Subsequently, incisional biopsy was taken. Histopathological examination and immunohistochemistry confirmed a high-grade plasmablastic neoplasm, favoring a diagnosis of PBL. Most of the reported cases of PBL have occurred in HIV-positive patients, and the bone is a very rare site. PBL can be confused with PBPCM. A final diagnosis should be rendered only after thorough histopathological and immunohistochemical examination.