Currently, low concordance (36%) is found between clinical complete response and pathologic complete response in patients with rectal cancer after neoadjuvant chemoradiotherapy. Probe-based confocal laser endoscopy (pCLE) provides a promising targeted optical biopsy to evaluate the response to neoadjuvant chemoradiotherapy. The aim of this study is to investigate whether pCLE-targeted optical biopsy can improve the accuracy of preoperative endoscopic biopsy for local rectal scars in rectal cancer patients after neoadjuvant chemoradiotherapy.

Patients with locally advanced rectal cancer can benefit from neoadjuvant chemoradiotherapy, and 20%-30% of patients receiving such therapy can attain a pathologic complete response, defined as the eradication of cancer cells. For those who reach pathologic complete response, a watch-and-wait strategy is supposed to be the best choice. However, low concordance (36%) was found between clinical complete response and pathologic complete response in patients with rectal cancer after neoadjuvant chemoradiotherapy. There is a compelling need to improve the consistency.

Probed-based confocal laser endoscopy (pCLE) is a novel endoscopic adjunct that allows real-time in vivo histological examination of mucosal surfaces. By using intravenous fluorescent agents, pCLE highlights certain mucosal elements that facilitate an optical biopsy in real time. It provides a promising targeted optical biopsy for local rectal scars in rectal cancer patients after neoadjuvant chemoradiotherapy.

The investigators perform this study to investigate whether pCLE-targeted optical biopsy could improve the accuracy of preoperative endoscopic biopsy for local rectal scars in rectal cancer patients after neoadjuvant chemoradiotherapy. In this study, rectal cancer patients after neoadjuvant chemoradiotherapy will be successively arranged to accept traditional endoscopic biopsy and pCLE-based targeted optical biopsy. The consistency rate will be calculated according to the postoperative pathological results.

Inclusion Criteria:

1. Age from over 18 to under 80 years
2. American Society of Anesthesiology(ASA) score class I,II,or III
3. Locally advanced rectal cancer
4. Patient has completed standard neoadjuvant therapy
5. Expected surgical resection
6. Written informed consent

Exclusion Criteria:

1. Pregnant or lactating women
2. Acute renal insufficiency or stage II to IV chronic renal insufficiency
3. Patients with allergic constitution