Organ Preservation in Rectal Adenocarcinoma Using Hypofractionated Pelvic Radiotherapy (Hypo-OPRA): A Phase II Clinical Trial

At McGill, SCRT is used routinely as a pre-operative radiotherapy schedule for locally advanced adenocarcinomas of the rectum. Likewise SCRT followed by chemotherapy is already used routinely at McGill as a pre-operative regimen for locally advanced rectal cancer with high risk features. Compelling registry data from Scandinavia shows that enduring clinical complete responses can be achieved after SCRT. To date, however, nearly all of the published data supporting a surveillance strategy in complete clinical responders is based on LCCRT. The present study proposes to explore further the organ preservation potential of SCRT.

Adopting a non-operative strategy in rectal cancer patients who achieve complete tumour regression avoids the risks of surgical morbidity and mortality, notably a sparing of the rectal sphincter muscles in the case of low-lying tumours and consequently avoidance of a permanent stoma.

Although multiple phase III trials support the routine use of SCRT in the pre-operative setting for locally advanced rectal adenocarcinoma, to date nearly all of the published data supporting a surveillance strategy in complete clinical responders is based on LCCRT. Compelling registry data from Scandinavia does show that enduring clinical complete responses can be achieved after short-course pelvic radiotherapy. Furthermore, the Rectal Cancer and Pre-operative Induction Therapy Followed by Dedicated Operation (RAPIDO) study demonstrated that, compared with LCCRT, SCRT followed by chemotherapy (SCRT-CH) has a higher pathologic complete response rate (29% versus 14%), less disease-related treatment failure, and superior distant metastasis-free survival.

Short-course pelvic radiotherapy with or without sequential chemotherapy can induce enduring clinical complete responders and the use of SCRT as part of a non-operative organ preservation strategy merits further prospective exploration. At McGill, SCRT is already used routinely as a pre-operative dose schedule for clinically node negative/N1 locally advanced adenocarcinomas of the rectum where downsizing is not required to achieve a sphincter sparing R0 resection. Likewise, since the publication of the RAPIDO trial, SCRT followed by FOLFOX/CAPOX chemotherapy has emerged as the preferred regimen at McGill for patients with high risk features (cT4 disease, cN2 and/or extramesorectal nodes, EMVI+, threatened or involved mesorectal fascia and/or sphincter muscles). The present phase II prospective study proposes to explore further the organ preservation potential of SCRT combined with a simultaneous integrated boost on sites of gross disease..