Watch and Wait in Patients With dMMR/MSI-H Distal Rectal Cancer Accessed Pathological Complete Response After PD-1 Monoclonal Antibody Therapy-an Open Label, Multicenter, Prospective Study (BASKET)
Immunotherapy has achieved significant therapeutic effect in DNA mismatch repair-deficient or microsatellite instability-high (dMMR/MSI-H) colorectal cancer (CRC) , more than fifty percent of dMMR/MSI-H CRC patients might get pathological complete response(pCR) after PD-1 monoclonal antibody treatment. For distant rectal cancer(RC), radical resection and neoadjuvant chemotherapy or chemoradiotherapy might cause lots of treatment cost,damage to defecation and sexual function, acute toxicity, chronic dysfunction, even loss of anus and psychological disorder. This study aims to evaluate the effect and safety of watch and wait in patients with dMMR/MSI-H distal RC accessed pCR after PD-1 monoclonal antibody therapy.
⁃ Preliminary inclusion criteria：
• Histological identified rectal adenocarcinoma,
• Tumor biopsy immunohistochemical (IHC) identified dMMR, including one or more deficient of the MSH1,MSH2,MSH6 and PMS2 protein expression and diagnosed as deficient mismatch repair(dMMR), or next generation sequencing identified (MSI-H)； MRI identified tumor inferior margin lower than peritoneal reflection,
• Clinical staging TxNxM0, with or without positive MRF, with or without positive EMVI,
• Staging method：all patients undergo rectal palpation, high resolution MRI ± transrectal Ultrasound examination，positive perienteric lymph node(LN): short diameter ≥10mm LN or LN with typical metastatic shape and MRI character, clinical data should be re-evaluated and judged by center evaluation group when there are contradictory stagings，distant metastasis were excluded by chest and abdominal enhanced CT and pelvic enhanced MRI,
• No intestinal obstruction symptom，or obstruction relieved after proximal colostomy,
• No rectal surgery history,
• No chemotherapy or radiotherapy history,
• No biopharmaceutical treatment history(such as monoclonal antibody), immunotherapy(such as anti PD-1antibody, anti PD-L1 antibody, anti PD-L2 antibody or anti CTLA-4), or other research drug treatment,
• Endocrinotherapy history restriction:No
• Informed consent assigned, Final inclusion criteria：
• Clinical complete response (cCR)(Chest,abdominal and pelvic enhanced CT or pelvic enhanced MRI or transrectal ultrasound proved)
• Transrectal ultrasound biopsy or endoscopic biopsy proved pathologically complete response (pCR)