Waiting for a sign.

Top Line: How long should you wait after neoadjuvant chemoradiation (CRT) for locally advanced rectal cancer to see a pathologic complete response (pCR)?

The Study: The pCR rate after standard, long-course chemoradiation for rectal cancer is around 15-20%. And while it’s pretty clear that a pCR is associated with better survival outcomes, it’s not clear if the treatment that induces a pCR leads to better outcomes or if the pCR is indicative of tumor biology that will have better outcomes anyway. Ignoring the latter question, it would at least be beneficial to know the optimal timing of surgery after CRT to identify pCR’s for prognostic purposes. This pooled analysis of individual patient data from over 3000 patients in 7 randomized trials analyzes the pCR rate in the context of the interval from CRT to surgery. The data spans nearly 20 years of trials. Over time, the median dose of radiation increased as did the median interval between CRT and surgery. Overall, 14.3% of patients achieved a pCR--which also increased over time from ~10% in the early 1990’s to ~15% in the early 2000’s and then to nearly 20% in the 2010’s. They found that the cumulative pCR rate rises between 4 and 11 weeks and eventually plateaus around week 16. By week 10, 95% of all pCR’s were achieved. Importantly, a longer interval between CRT and surgery was not associated with inferior treatment outcomes. 

TBL: After standard neoadjuvant chemoradiation for rectal cancer, a 10 week interval is needed to identify 95% of pathologic complete responders. | Gambacorta, Radiother Oncol 2020

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