The investigators evaluate the response of rectal cancer to neoadjuvant therapy and classify the response according to specific periods of time after the end of neoadjuvant treatment.

In the treatment of locally advanced rectal cancer, an optimal interval between neoadjuvant therapy and surgery might improve oncological outcomes. Besides, those patients who achieve a good response might benefit from active surveillance, avoiding surgical comorbidities. This optimal interval is yet to be defined. This study will aim to better define the role of time interval between the end of neoadjuvant therapy (NAT) and TME in Spanish regions, together with analyzing the importance of restaging MRI and define the basis for implementing a "watch and wait" protocol.

Inclusion Criteria:

• Adult patients suitable for elective surgical resection of biopsy-confirmed rectal adenocarcinoma (0-15 cm from the anal verge) determined by rectal cancer protocol magnetic resonance imaging.
• Patients treated with long-course neoadjuvant chemoradiotherapy (nCRT).
• Patients treated with short-course radiotherapy with delayed surgery.
• Clinical stage IIA, IIB, IIIA, IIIB, IIIC (cT3/cT4, or cN1/cN2 with any cT, M0) determined by rectal cancer protocol magnetic resonance imaging

Exclusion Criteria:

• Intolerance or contraindication to planned NAT.
• Patients who have not finished NAT for any reason.
• Patients with unknown cT or cM.
• Tumors previously treated with local excision or with distant metastatic disease.

This was a national multicentre retrospective cohort study. Participating centres are tertiary referral hospitals from different Spanish regions, which agreed to enter information in a standardized database, of all patients in their institute who had biopsy-confirmed rectal adenocarcinoma and had received neoadjuvant therapy. All patients with low, mid and high rectal cancer (0-15 cm from the anal verge), at a clinical stage IIA, IIB, IIIA, IIIB, IIIC (cT3/cT4, or cN1/cN2 with any cT, M0) will be included.