[A Patient with Cancer of Unknown Primary Who Responded to Chemotherapy].

Cancer of unknown primary is a class of malignant tumors, histologically identified as metastatic lesions whose primary origin is unknown despite adequate investigations for the primary tumor. Although the prognosis of cancer of unknown primary is generally poor, here, we report our experience with a patient who responded to chemotherapy. The patient was a 78-year-old woman. She had a history of gastric cancer at the age of 76 years. In June of year X-1, she was diagnosed with gastric cancer(tub1>tub2, pT1bN0M0, pStage Ⅰa)and underwent distal gastrectomy. One year after surgery, computed tomography revealed right supraclavicular lymphadenopathy, for which cervical lymphadenectomy was performed. The pathological diagnosis was ductal carcinoma with comedo necrosis and poorly differentiated solid adenocarcinoma that were suggestive of metastases from breast cancer. However, a detailed examination of the mammary glands revealed no mass. Imaging studies led to a diagnosis of cancer of unknown primary. Therefore, chemotherapy, according to the treatment of pancreatic cancer, was planned based on immunostaining, tumor markers, etc. Chemotherapy response evaluation after completing 4 courses demonstrated a partial response; the patient responded to the chemotherapy. We considered that estimating primary lesions from histopathological images, tumor markers, etc., may help determine effective chemotherapy regimens.