Prognostic influence of histopathological regression patterns in rectal adenocarcinoma receiving neoadjuvant therapy

Neoadjuvant chemoradiation therapy (CRT) followed by surgical resection has become the standard therapy for patients with locally-advanced rectal adenocarcinoma (1). This therapy has improved the outcome of these patients (2), but not all the cases show a good response to it and some patients might even progress during CRT with the consequent risks of tumor dissemination. There is much interest in developing systems that can predict response to therapy and also that can guide the need of adjuvant therapy after CRT. One of the factors that has been widely analyzed is pathological response to therapy. There are many systems to grade response. Initially most systems included five categories (3), but subsequent analysis concluded that three-tiered systems could correlate better with prognosis (4). The American Joint Committee on Cancer/College of American Pathologists (AJCC/CAP) recommended in 2010 to use a three tiered-system that considers the relative proportion of fibrosis and viable tumor cells, as proposed by Ryan et al. (4,5). Many authors have analyzed the prognostic significance of the different pathologic response grading systems with varying results (6,7), but very few studies have compared the different response patterns found in the tumor. The aim of this study is to analyze the pathologic response in our series of 183 patients from two Spanish hospitals and to determine whether there are different patterns of response and their prognostic significance