Multiple Myeloma Presenting as a Pancoast-Like Tumor: A Diagnostic Challenge

Apical lung masses are classically attributed to bronchogenic carcinoma, particularly superior sulcus (Pancoast) tumors. However, other entities may mimic this presentation. We report the case of a 68-year-old man, a former smoker, referred for progressive fatigue and lower limb edema, with normocytic anemia and an elevated erythrocyte sedimentation rate. Thoracoabdominal computed tomography revealed a 4.5-cm solid mass in the right lung apex with rib destruction and T2 vertebral body involvement, suggestive of a Pancoast tumor. Positron emission tomography demonstrated intense fluorodeoxyglucose (FDG) uptake (maximum standardized uptake value (SUV_max) 11.3) and a hypermetabolic osteolytic lesion at T10. CT-guided transthoracic biopsy revealed infiltration by atypical plasma cells, CD138-positive and thyroid transcription factor 1 (TTF-1)-negative, with lambda light chain restriction. Bone marrow evaluation confirmed multiple myeloma. This case underscores the importance of histopathological confirmation in apical masses and the need to include multiple myeloma in the differential diagnosis, particularly when systemic hematologic abnormalities are present.