MR prediction of pathologic complete response and early-stage rectal cancer after neoadjuvant chemoradiation in patients with clinical T1/T2 rectal cancer for organ saving strategy.

To evaluate the ability of magnetic resonance imaging (MRI) to predict pathologic complete response (pCR) after neoadjuvant chemoradiation therapy (CRT) in patients with clinical T1/T2 rectal cancer to indicate candidates for organ-saving strategies.Between 2012 and 2016, 38 patients with clinical T1/T2 rectal cancer received neoadjuvant CRT. Radiologic complete response (rCR) was assigned when dense fibrotic tissue without tumor signal intensity was observed on post-CRT MRI. Surgical pathologic assessment was used to evaluate tumor regression. The association between rCR and the mural extent of the primary tumor, pCR, and pathologic T stage were analyzed.In rCR patients, the pCR rate was higher; the odds of achieving pCR were 8.00 times higher than for non-rCR patients (P = .02). rCR patients were also more likely to have early-stage cancer than non-rCR patients (P = 0.01). Patients with partial extent of the primary tumor on post-CRT MRI were more likely to be diagnosed with early-stage cancer than those with transmural extent (P = .01).rCR indicated by post-CRT MRI can be used as a supportive factor to predict pCR after neoadjuvant CRT in patients with clinical T1/T2 rectal cancer and can guide management decisions around organ-saving treatments.