Skeletal Muscle Metastasis from Colorectal Cancer: Report of a Case

Metastases from colorectal cancer can occur by either lymphatic or hematogenous spread, and the sites most commonly involved are the liver and lung. Although skeletal muscle comprises a considerable portion of body mass and receives abundant blood supply, it is one of the most unusual sites of metastasis from any malignancies. We report a case of skeletal muscle metastasis from colorectal cancer. An 83-year-old female patient presented with a painful mass in the right posterior thigh. She had already undergone low anterior resection and right lobectomy of liver for rectal cancer with liver metastasis (T2N1M1) about 4 years ago. Although a follow-up computed tomography scan showed a metastatic solitary pulmonary nodule in the left lobe 2 years after the primary operation, she refused further aggressive treatment. Magnetic resonance imaging showed a localized mass in the semimembranosus muscle of the right thigh, and fine-needle aspiration cytology demonstrated clusters of atypical cells compatible with adenocarcinoma. The patient underwent excision of the painful mass located in the right semimembranosus muscle. Histologically, the thigh mass proved to be adenocarcinoma identical to the primary lesion. The patient died of heart failure on the 2nd postoperative day.