Association of adjuvant chemotherapy with improved overall survival for patients with locally advanced rectal cancer (LARC) who achieve a pathologic complete response (pCR) to neoadjuvant chemoradiation (nCRT).

Abstract

716 Background: 15-20% of patients with locally advanced rectal adenocarcinoma (LARC) achieve a pathologic complete response (pCR) following neoadjuvant chemoradiation (nCRT). The role of adjuvant chemotherapy has been questioned. Methods: Patients with rectal cancer receiving nCRT in the National Cancer Data Base (NCDB) 2006-2013 data set were evaluated. The primary outcome was overall survival (OS). The association between OS and patient characteristics were examined using multivariable Cox regression models. Results: 2,903 patients were identified who achieved a pCR. The median follow up was 43.2 months. 2,102 received nCRT and 789 received nCRT + adjuvant chemotherapy. Factors significantly associated with OS included age (p<0.001), gender (p=0.011), Charlson-Deyo comorbidity score (CDI) (p<0.001), grade (p=0.029), clinical T stage (p=0.030), and CEA negativity (p=0.002), but not nodal status. The 3-year OS rate was 94% in the adjuvant therapy group as compared to 84% in the nCRT alone group (p<0.001). In considering clinical N-stage, the benefit was comparable for both N+ and N- tumors. Adjuvant chemotherapy was more likely to be given for younger patients (age < 60), lower comorbidity score, higher grade, positive CEA status, higher clinical T stage, and higher clinical N stage. When stratifying by these factors, similar benefits in OS were observed in the adjuvant cohort. Conclusions: Following nCRT and achievement of a pCR, the receipt of adjuvant chemotherapy is associated with improved OS. Patients receiving adjuvant therapy were more likely to be younger and have a low CDI, but have more advanced stage disease. Thus, a selection bias may be present. Nonetheless, in the setting of the already excellent outcome associated with pCR, the additional benefit of adjuvant chemotherapy should be weighed against toxicity.