Occult breast cancer with pleural metastasis

Carcinoma of unknown primary (CUP) is defined as histologically confirmed metastases from an undetectable malignant primary site. A subgroup of CUP, known as occult breast cancer (OBC), is a biopsy-proven metastatic breast cancer without an original breast tumor. It remains a diagnostic and therapeutic enigma as there is no consensus on the diagnostic and treatment approaches for the patients with OBC. This case report is a unique presentation of OBC, emphasizing the importance of identifying OBC patients in the early stages. A dedicated team of experts and a more definitive approach to diagnosis and treatment of OBC are essential to prevent delays in the whole process.