Oligometastatic Rectal Adenocarcinoma Treated With Short-Course Radiotherapy and Chemotherapy with Non-Operative Intent of the Primary for Pelvic Complete Responders

Abstract

Sequential short-course radiotherapy and chemotherapy (SCRT-CH) is a promising treatment for non-operative management of rectal adenocarcinoma. This paradigm has not been evaluated for newly diagnosed oligometastatic (OM1) patients (pts). We evaluated rates of locoregional clinical complete response (cCR), rectal surgeries, and local control (LC) in newly diagnosed OM1 pts treated with definitive treatment of the primary tumor with SCRT-CH with non-operative intent for pts with locoregional cCR.From 2/2018 to 5/2020, 39 pts with newly diagnosed OM1 rectal cancer were treated with SCRT-CH and non-operative intent for locoregional cCR at a single institution. OM1 disease was considered disease confined to ≤ 2 distant sites. Pts received 25 Gy/5 fx to the pelvis with an optional boost to 35 Gy for involved extra-mesorectal lymph nodes. CH was delivered prior to and/or after RT. Locoregional cCR was assessed via DRE, sigmoidoscopy, and/or pelvic MRI following completion of SCRT-CH. Follow-up was calculated from RT completion. Survival was evaluated by Kaplan-Meier method and log rank test.All 39 pts with 47 distant sites completed SCRT and 36 (92%) had CH. 22 (56%) received all CH following RT, and 24 (62%) received at least 2 months of CH after RT. 33 pts received 1st line FOLFOX +/- bevacizumab (bev). 13 pts underwent low anterior resection and 2 pts underwent abdominoperineal resection. 19 pts had 23 distant sites treated. The most common distant site treated was liver and the most common modality was resection. Following SCRT, only 4 pts (10%) experienced a local failure (median 6.4 months, range 0.7-10.7 months). 6/39 experienced a pelvic cCR (15%); all cCR pts received SCRT first followed by at least 2 months of CH. Pts with a cCR were more likely to have received at least 2 months of CH following SCRT compared to patients without a cCR (100% vs. 59%, P < .05). The median follow-up for living pts was 16 months. The 1-year overall survival (OS) was 66% (95% CI: 51-84%) for all pts. Pts who received at least 2 months of CH following SCRT had an improved OS (1-year OS [95% CI]: 82% [68-100%] vs. 29% [10-84%], P < .001 by log-rank) compared to pts who did not.SCRT-CH with non-operative intent for pts in locoregional cCR is a promising treatment paradigm for OM1 rectal cancer pts.