Why do rectal cancer patients wait 6 weeks after chemoradiation therapy before having surgery?

This study summarized current data on the optimal interval between chemoradiation therapy and surgery for rectal cancer patients.

Locally advanced rectal cancer indicates that the cancer has spread beyond the lining of the rectum or has spread to the nearby lymph nodes. The standard treatment for low-lying locally advanced rectal cancer consists of chemoradiation therapy and surgery 6 weeks later to remove the tumor. However, it is possible that waiting slightly longer may further benefit patients.

This study reviewed recent articles that investigated the impact of timing of surgery on patient outcome.

Why is it standard practice to wait for 6 weeks?

The length of the interval varied for many years, until Lyon and colleagues published an article in 1999. They reported that patients who waited 6 weeks for surgery had a better response than patients who only waited 2 weeks. As a result of this report, a 6-week interval between chemoradiation and surgery became standard practice.

The interval length needs to be carefully balanced. It is understood that the wait should be long enough to allow for the tumor to shrink and for the surrounding tissue to recover. However, the wait should not be long enough for the tumor to progress or spread to other sites (metastasis).

Should the wait be longer than 6 weeks?

Several recent retrospective studies (studies based on patient records) have examined whether increasing the interval to 8 or 12 weeks can improve patient outcome. Some reported that prolonging the interval may lead to higher rates of tumor downstaging (shrinking of the tumor). For example, one study reported a significantly higher tumor response for the long-interval group (71%) than for the shorter interval group (53.1%). A second study reported a significant increase in tumor downstaging and complete responses (the tumor had disappeared) following a longer interval prior to surgery (25%) compared to shorter intervals (18%). These improvements were reported to occur without any increases in surgical difficulty or complications.

It has been suggested that the improvements could increase patient survival and prolong disease-free survival (length of time after primary treatment for a cancer ends that the patient survives without any signs or symptoms of that cancer). One study, for instance, reported significantly higher overall survival rates (time until death from any cause) in the long-interval group (93%) compared to the shorter-interval group (81%), and a significantly lower distant metastatis rate (6%, compared to 19% in the short-intervel group). 

The authors concluded that new research has prompted a trend towards longer intervals between chemoradiation therapy and surgery. However, they highlight that further research is needed to ensure that longer intervals really benefit patients.

The results mainly come from retrospective studies. Clinical trials are currently being carried out which should clarify the issue.