Background: The presentation of gastric carcinoma with a metastasis in skeletal muscle is a distinct rarity.
Case report: In a 72-year-old male patient a soft tissue mass behind the knee was biopsied rather late. Histology showed a metastasis of adenocarcinoma. The patient mentioned a slight feeling of strangulation, which led to endoscopy and the diagnosis of gastric carcinoma. Palliative chemotherapy was initially successful but the patient died after 21 months.
Discussion: Based on this case history, three points are discussed: how to biopsy a peripheral soft tissue mass, how to proceed when a metastasis of an unknown primary tumor is diagnosed, and the epidemiology of metastases to skeletal muscle.