Pathological complete response after neoadjuvant therapy for rectal cancer and the role of adjuvant therapy

Both the addition of neoadjuvant chemoradiation therapy and improvements in surgical techniques have improved local control and overall survival for locally advanced rectal cancer patients over the past few decades. The addition of adjuvant chemotherapy has likely improved outcomes as well, though the contribution has been more difficult to quantify. At present, the majority of resected locally advanced rectal cancer patients receive adjuvant chemotherapy, though there is great variability in this practice based on both patient and institution characteristics. Recently, questions have been raised regarding which sub-groups of patients benefit most from adjuvant chemotherapy. As pathologic complete response (pCR) is increasingly found to be a reasonable surrogate for long-term favorable outcomes, some have questioned the need for adjuvant therapy in this select group of patients. Multiple retrospective analyses have shown minimal to no benefit for adjuvant chemotherapy in this group. Indeed, the patients most consistently shown to benefit from adjuvant therapy both in terms of disease free survival (DFS) and overall survival (OS) are those who achieve an intermediate pathologic response to neoadjuvant treatment. Tumors that have high expression of thymidylate synthetase have also shown to benefit from adjuvant therapy. More study is needed into clinical and molecular features that predict patient benefit from adjuvant therapy.