# Case Report: A rare solitary peroneus longus metastasis from rectal cancer managed with multimodal therapy

## TL;DR

A rare case of rectal cancer spreading to a leg muscle was successfully treated with surgery and chemotherapy, showing the importance of individualized care.

## Contribution

This case report presents a rare instance of rectal cancer metastasis to the peroneus longus muscle and its successful multimodal treatment.

## Key findings

- A patient with rectal cancer developed a solitary metastasis in the peroneus longus muscle three months after surgery.
- Combined treatment with surgery and chemotherapy led to no recurrence or further metastasis over 30 months.
- The case highlights the need for clinical awareness of rare skeletal muscle metastases from rectal cancer.

## Abstract

Solitary skeletal muscle metastasis from rectal cancer is exceptionally rare and carries a generally poor prognosis, with no established treatment guidelines currently available. We present a case of a patient with advanced rectal cancer (T3cN2bM0) who refused recommended neoadjuvant chemoradiotherapy and underwent laparoscopic radical resection alone. Subsequently, the patient developed an isolated metastasis to the left peroneus longus muscle merely three months postoperatively. The metastasis presented as a painful mass, and 18F-Fluorodeoxyglucose positron emission tomography/ computed tomography (18F-FDG PET/CT) revealed its hypermetabolic nature, suggesting malignancy. This suspicion was confirmed histopathological, establishing the diagnosis of skeletal muscle metastasis from rectal adenocarcinoma. Following a combined treatment of surgical resection and systemic chemotherapy, the patient remarkably remained free of local recurrence or further metastasis throughout a 30-month follow-up period. This case underscores the importance of clinical alertness for rare skeletal muscle metastases and highlights that individualized treatment is essential for improving patient prognosis.