Skeletal Muscle Metastases from Colorectal Adenocarcinoma: A Rare Case Report with Literature Review

Background and Clinical Significance: Colorectal cancer (CRC) is the third most common cancer worldwide and the second leading cause of cancer-related death. Skeletal muscle metastases are extremely rare and typically occur in advanced or poorly differentiated tumors. In selected oligometastatic cases, surgical excision can provide symptom relief and requires a multidisciplinary approach. Case Presentation: We report a 73-year-old female patient with colonic adenocarcinoma treated with right hemicolectomy and side-to-side mechanical anastomosis, followed by adjuvant CAPOX chemotherapy. The tumor was characterized by MSI-H (microsatellite instability-high) status. During adjuvant treatment (less than 6 months after surgery), she developed progressive right thigh pain, later diagnosed as an intramuscular skeletal muscle metastasis measuring approximately 16 × 13 × 8 cm. The patient underwent en bloc resection of the tumor, followed by adjuvant chemotherapy after metastasectomy. Upon disease progression, first-line chemotherapy in combination with targeted therapy (bevacizumab) was administered. Conclusions: Skeletal muscle metastases from colorectal adenocarcinoma are rare. This case emphasizes the importance of recognizing atypical metastatic patterns and suggests that, in selected oligometastatic cases, surgical excision combined with a multidisciplinary approach may improve symptom control and clinical outcomes.