Abstract: Synchronous metastasis of rectal cancer accounts for 16%-20% of newly diagnosed rectal cancer. Of these patients with lower tumor burden received simultaneous or staged radical resection in both primary and metastases tumor could prolong overall survival. For these patients， pre-or post-operative pelvic radiotherapy improved locoregional control and the 2-year local recurrent rate was only 0-11％， but the majority （56％-75％） of recurrences occurred in distant organs， and radiotherapy did not improve 2-year overall survival rate of 65％-80％. For the patients with high tumor burden， the primary and metastases tumor could not be removed through surgical resection or local-directed therapy including radiofrequency ablation or transarterial chemoembolization. Of these patients， palliative radiotherapy could relieve symptomatic respose rate （bleeding， pain or obstruction） in 80％-85％ patients and last for a long term avoiding unnecessary colostomy. Short course radiotherapy of 5×5 Gy， which had advantages including short treatment time， lower toxicities， similar efficacy as long course radiotherapy and without delay of surgery or systemic chemotherapy should be the optimal radiation method for patients with synchronous metastases rectal cancer.

Key words: Rectal cancer, Synchronous metastases, Radiotherapy