Signet ring cell histology and non-circumferential tumors predict pathological complete response following neoadjuvant chemoradiation in rectal cancers

Neoadjuvant chemoradiation followed by surgery is now the standard of care for patients with locally advanced rectal cancers. The aim of this study was to determine the rate of pathological complete response (pCR) following neoadjuvant treatment in patients with rectal cancers and identify the factors predicting the same. We conducted a retrospective analysis of patients with rectal cancers treated with neoadjuvant therapy followed by surgery at our institution from 1993 to 2008. Patients who achieved pCR were identified. Various patient, tumor, and treatment-related factors were studied for their influence on pCR by univariate and multivariate analyses. The influence of pCR on survival was also studied but was restricted to patients with a minimum follow-up of 5 years. Between 1993 and 2008, 248 patients with rectal cancers received neoadjuvant therapy followed by surgery. Two hundred and twenty-seven patients received chemoradiation and 21 patients received only radiation. Pathological complete response was seen in 32 patients (12.9%). On multivariate analysis, the factors found to be independently predictive of pathological response were circumferential extent of the primary tumor (p = 0.016) and signet ring cell histology (p = 0.001). Among 116 patients with a minimum follow-up of 5 years, there was a trend towards increased overall survival (75% versus 54%) and reduced local recurrence (6.2%versus 12.3%) in the 16 patients who achieved a pCR compared to those who did not, even though the difference was not statistically significant. The factors that predict a pCR after neoadjuvant treatment for rectal cancers are absence of circumferential involvement and signet ring cell histology. Pathological complete response may confer an insignificant survival advantage.