The effect of the time interval between radiotherapy and surgery on the recurrence of breast cancer has been investigated in several countries. Some studies have indicated a positive association,1 2 whereas others have found no link.3 4 A recent systematic review concluded that an interval of more than eight to 12 weeks between breast conserving surgery and radiotherapy increased local recurrence rates when no other treatment was given.5 However, the review summarised studies that had used different cut-off points for time to radiotherapy, which hampers a straightforward interpretation.

In the linked retrospective cohort analysis (doi:10.1136/bmj.c845), Punglia and colleagues assess whether the interval between breast conserving surgery and radiotherapy affects the risk of local recurrence in women with early stage breast cancer in the United States.6 They found a significantly increased hazard of local recurrence of breast cancer in women who waited more than six weeks for radiotherapy (hazard ratio 1.19, 95% …