Rates of reoperation after breast conserving cancer surgery in Western Australia before and after publication of the SSO-ASTRO margins guideline.

Abstract

A 2014 SSO-ASTRO guideline on surgical margins aimed to reduce unnecessary reoperation after breast conserving surgery (BCS). We investigate whether publication of the guideline was associated with a reduction in reoperation in Western Australia (WA). In this retrospective, population-based cohort study, cases of newly-diagnosed breast cancer were identified from the WA Cancer Registry. Linkage to the Hospital Morbidity Data Collection identified index BCS for invasive cancer between January 2009 and June 2018 (N=8059) and reoperation within 90 days. Pre-guideline (2009-2013) and post-guideline (2014-2018) reoperation proportions were compared, and temporal trends were estimated with generalised linear regression. The pre-guideline reoperation proportion was 25.8% compared with 21.7% post-guideline (difference -4.0% [95% CI -5.9, -2.2, p<0.001], odds ratio [OR] 0.80 [95% CI 0.72, 0.89, p<0.001]). Absolute reductions were similar for repeat BCS (16.3% versus 14.6%; difference -1.8% [95% CI -3.4, -0.2, p=0.03]) and conversion to mastectomy (9.4% versus 7.2%; difference -2.2% [95% CI -3.4, -1.0, p<0.001]). Over the study period, there was an annual absolute change in reoperation of -0.8% (95% CI -1.2, -0.5, p<0.001). Accounting for this linear trend, the difference in reoperation between time periods was -0.5% (95% CI -4.3, 3.3; p=0.81), reflecting a non-significant reduction in conversion to mastectomy. Comparisons of pre- versus post-guideline time periods in WA showed reductions in reoperation that were similar to international estimates; however, an annual decline in reoperation predated the guideline. Analyses that do not account for temporal trends are likely to overestimate changes in reoperation associated with the guideline.