Bone metastatic carcinoma coexisting with plasma cell myeloma: a case report.

OBJECTIVE: Multiple myeloma is a clonal plasma cell proliferation often causing bone lytic lesions. It is sometimes challenging to differentiate these lytic lesions associated with multiple myeloma from bone destruction due to a metastasis. Although coexistence of solid tumors and plasma cell myeloma in one patient has been described, synchronous skeletal metastases from both neoplasms occurring in the same bone lesion is exceptional. Indeed, only one case has been reported in the literature. CASE PRESENTATION: Herein, we report a case involving a 68-year-old Caucasian male patient admitted to our department for coronavirus disease 2019 infection with incidental finding of multiple lytic bone lesions during hospitalization. Laboratory tests revealed an increased immunoglobulin G kappa M protein and high levels of carbohydrate antigen 19-9. Bone marrow aspiration showed increased atypical plasma cells consistent with multiple myeloma. Percutaneous image-guided biopsy of one of the osteolytic lesions was performed. Pathological examination identified both plasma cell neoplasm and poorly differentiated metastatic carcinoma within the same bone lytic lesions. CONCLUSION: The present case raises awareness among clinicians and pathologists that clinical and radiologic suspicion of multiple myeloma may be within the spectrum of second primary malignancies.