Preoperative radiotherapy for select T4 primary and locally recurrent colon cancers: Experience from an Australian quaternary centre.

Abstract

e15656 Background: We report our experience with preoperative radiotherapy for select T4 primary or locally recurrent colon cancers in a single, quaternary institution. Methods: A total of 89 patients with T4 primary (n = 40) and locally recurrent (n = 49) adenocarcinoma of the colon ( > 15 cm from the anal verge) underwent preoperative-intent radiotherapy in our centre from 2005 to 2020. Majority of the tumours arose from the sigmoid, 79% (n = 29) for the T4 primary group and 68% (n = 32) for the locally recurrent group. The most common tumour sites prior to preoperative radiotherapy in the locally recurrent group were the lateral pelvic brim (n = 24; left = 16; right = 8), and the proximal presacral area (n = 13). Of the evaluable patients, 95.8% (23/24) of the T4 primary group and 91.3% (21/23) of the locally recurrent group were MMR-proficient. Preoperative radiotherapy prescription was 45-50.4 Gy given in 1.8-2 Gy per fraction. Concurrent 5-FU based chemotherapy was given in 95% (n = 38) of the T4 primary group and 95.9% (n = 47) locally recurrent group. Median follow-up time was 48.9 months (range, 31.5- 80.7) for the T4 primary group and 43.1 months (range, 24.2- 74.1) for the locally recurrent group. Results: In the T4 primary group, downstaging of the pre-treatment clinical stage was documented in 57.5% (n = 23) and curative-intent surgery was possible in 90% (n = 36), 80.5% (n = 29) of which were R0 resections. On the other hand, curative-intent surgery was possible in 79.6% (n = 39) of the locally recurrent group, 64% (n = 25) of which were R0 resections. Of the patients who underwent surgery, 22% (n = 8) in the T4 primary group and 41% (n = 16) in the locally recurrent group avoided a multi-visceral resection. A pathologic complete response was achieved in 8.3% (n = 3) in the T4 primary group and in 10.3% (n = 4) in the locally recurrent group. For the T4 primary group, 13% had local failures (Hazard rate 3%, 95% CI 1-6%), 38% had any disease progression (Hazard Rate 9%; 95% CI 5-14), and 45% died (Hazard Rate 8%; 95% CI 5-13) during the follow-up period. For the locally recurrent group, 35% had local failures (Hazard Rate 13%, 95 CI 9-19), 61% had any disease progression (Hazard Rate 20%, 95% CI 14-29), and 60% died (13%, 95% CI 9-19) the follow-up period. Grade 1-2 anastomotic leak occurred in a total of 6 (8%) patients, 3 in each group. Readmission after surgery was needed in a total of 17 (22.6%) patients, 4 in the T4 primary group and 13 in the locally recurrent group. There was no 30-day mortality in the entire cohort. Conclusions: Curative-intent resection may be achieved after preoperative radiotherapy for select T4 primary and locally recurrent colon cancer, which may translate in encouraging clinical outcomes for an advanced cohort of patients. Careful patient selection is required to identify which colon cancer patients may benefit with preoperative radiotherapy.