Pleomorphic rhabdomyosarcoma of the left lower extremity with synchronous gastric and small intestinal metastases presenting as intussusception: a case report.

BACKGROUND: Pleomorphic rhabdomyosarcoma (PRMS) is a rare and highly malignant soft tissue sarcoma in adults. Gastrointestinal metastasis is uncommon, and simultaneous involvement of the stomach and small intestine manifesting as intussusception is extremely rare. Early clinical manifestations are insidious and easily misdiagnosed. CASE PRESENTATION: A 62-year-old male patient was admitted on February 8, 2025, due to "postprandial abdominal fullness and discomfort for more than 1 month, aggravated with nausea and vomiting for more than 10 days". He noticed a mass in his left lower leg in January 2023, and underwent mass resection at an outside hospital in December 2023. Postoperative pathology suggested spindle cell rhabdomyosarcoma (RMS). Early tumor recurrence occurred after surgery, and he was admitted to The Affiliated Hospital of Southwest Medical University in January 2024. PRMS was confirmed by pathological consultation, and he received 3 cycles of anthracycline-ifosfamide (AI) regimen chemotherapy. Due to disease progression, left lower extremity amputation was performed in December 2024. The current admission revealed multiple metastases to the stomach and small intestine complicated with intussusception and intestinal obstruction. Emergency partial small bowel resection was performed, and metastatic PRMS was confirmed by postoperative pathology and Immunohistochemistry (IHC). The patient recovered smoothly after surgery. CONCLUSIONS: Adult PRMS is highly malignant with poor chemosensitivity. Synchronous gastric and small intestinal metastases causing intussusception is extremely rare. This case also highlights the critical impact of fragmented care, specifically the lack of adjuvant therapy post-resection and inadequate systemic staging prior to amputation, on disease progression.​ Clinicians should maintain high vigilance for unexplained gastrointestinal symptoms in patients with a history of sarcoma, establish an early diagnosis based on pathology and IHC, and advocate for continuous, standardized, multidisciplinary management​ to improve prognosis.