This study aimed to assess the clinical outcomes of neoadjuvant modified short-course radiotherapy (mSC-RT) for rectal metastatic adenocarcinoma.

Data from 14 patients who underwent mSC-RT followed by surgery for primary tumors were retrospectively analyzed. Twelve patients received systemic chemotherapy for 18 weeks. A 2.5 Gy dose twice daily, up to a total dose of 25 Gy in 10 fractions, over 5 consecutive days was administered through mSC-RT. Surgery for primary tumor was performed five weeks (range=3-7 weeks) after mSC-RT. Nine patients underwent adjuvant chemotherapy. The median follow-up was 38.5 months.

No patients developed grade ≥3 toxicities before surgery. Three patients developed local failures and 10 died during the follow-up period. The 1-, and 3-year local control rates were 91.7% and 71.3%, respectively. The median overall survival (OS) was 45.1 months. The 1-, and 3-year OS rates were 85.7% and 56.3%, respectively. Patients with stage IVA showed significantly better OS than those with stage IVB disease.

mSC-RT followed by delayed surgery was well-tolerated and led to good local control in patients with rectal metastatic adenocarcinoma. mSC-RT could be a treatment option for patients with rectal metastatic adenocarcinoma as it is less likely to lead to cessation of systemic chemotherapy.