Squamous Cell Carcinoma of Unknown Primary that Metastasized to an Inguinal Lymph Node: A Case Report

Carcinoma of unknown primary (CUP) is a malignant tumor with histological characteristics indicating metastasis in a patient with an unidentified primary lesion after whole-body evaluation at the time of examination. CUP incidence is similar in men and women, and average age at diagnosis is 60 years. Re-ports of overall incidence vary but CUP is believed to account for 1-5% of all cancers. We encountered a case of apparently metastatic squamous cell carcinoma of the inguinal region in a patient without a de-tectable primary lesion. We report this case and review the literature on CUP, to increase awareness of this rare lesion. (J Nippon Med Sch 2022; 89: 454?459)