Metformin With Neoadjuvant Chemoradiation to Improve Pathologic Response in Rectal Cancer: a Pilot Phase I/II Trial

Abstract

Background: Neoadjuvant radiotherapy with or without chemotherapy decreases the risk of local recurrence after surgery for stage II or III rectal cancer. Emerging data suggest that diabetic patients on metformin may have improved cancer outcome after radiotherapy. We asked if metformin given concurrently with long course chemoradiation (CRT) may improve pathologic complete response (pCR) in non-diabetic rectal cancer patients. A single-institutional pilot study was performed to build a confidence interval for the pCR rate and to determine the sample size for a phase 2 trial.Methods: Non-diabetic patients with biopsy confirmed adenocarcinoma of the rectum, and deemed candidates for long course neoadjuvant CRT were invited to participate. Radiation consisted of 50.4 Gy in 28 daily fractions. Capecitabine (825 mg/m2 twice daily, Monday-Friday) was self-administered during the 28 days of radiation only. The primary outcome was pCR. The study was designed to accrue 15 participants to construct a confidence interval (CI) for the pCR rate. Results: A total of 16 patients were accrued from January 2017 to May 2018. One patient withdrew from the study prior to CRT. Only grade 1 or 2 adverse events were observed from the intervention. Three patients had a clinical complete response (cCR) and did not have surgical resection. Of the 12 patients who underwent surgery, there were two pCRs. For the combined pCR/cCR rate of 33% (95% CI 19-47%), a total of 85 patients will be required to yield a 95% CI with a 10% margin of error. Conclusions: Adding metformin to neoadjuvant CRT for rectal cancer does not appear to enhance toxicities. These results will be used to refine the design and conduct of a future phase 2 trial to determine whether adding metformin to CRT improves pCR/cCR rates. Trial registration: NCT03053544. Registered December 20, 2016, https://clinicaltrials.gov/ct2/show/record/NCT03053544