The risk of distant metastases in rectal cancer managed by a watch-and-wait strategy - A systematic review and meta-analysis.

Background: The watch-and-wait (w&w) strategy is associated with frequent local regrowth (LR). Distant metastases (DM) occur more often in the patients with LR than in those without. However, it is unknown whether omitting immediate surgery results in the additional risk of DM.

Materials/methods: A systematic review and meta-analysis were performed to determine the maximum risk of additional DM. To estimate this, we used data showing the proportions of DM in patients with and without LR, assuming that the excess DM in patients with LR may develop in two ways: from subclinical DM already present at baseline and due to seeding from the uncontrolled primary tumor, and that the incidence of subclinical DM at baseline in the LR subgroup is at least not lower than in the non-LR subgroup. Based on the calculated rate of excess DM in the LR subgroup we have obtained the rate for the whole group of patients undergoing w&w.

Results: The maximum estimated risk of additional DM was 3.0% (95% CI: 1.2-4.9%) in the total group. After correction for short follow-up, the maximum risk at 5 years was 6.5%. Thus, the risk of excess DM is between 0% and 6.5%. Other evidence from a systematic review and the conservative assumptions taken for the calculation of the correction suggest that this maximum risk may be overestimated.

Conclusions: The additional risk of DM seems to be low. However, the high probability of bias, heterogeneity of the patients' population and low quality of evidence make our estimation uncertain.