Searching for the Culprit: Metastases from a Cancer of Unknown Primary.

We report a case of metastases from a cancer of unknown primary whose primary site could not be identified during the appropriate pretreatment evaluation. The patient was a 58-year-old woman with a history of passive smoking and with no history of cancer in the family. Her current condition started with asthenia, adynamia, and pallor, followed by palpitations. An abdominopelvic computed tomography (CT) scan was performed, showing multiple osteolytic lesions distributed in all bone structures and axillary adenopathy on the left side. As part of the approach and given the high suspicion of multiple myeloma, tests were performed. The results were negative for multiple myeloma. A PET-CT scan was performed and showed left axillary adenopathy. The breasts and other organs were not affected. Left axillary lymph node resection revealed breast primary metastatic pleomorphic lobular carcinoma. Due to the metastatic disease (caused by the primary breast cancer), it was decided to start chemotherapy.