Effects of specialisation on treatment and outcomes in screen-detected breast cancers in Wales: cohort study.

Volume-outcome relationships have been found for management of symptomatic but not for screen-detected, breast cancers. The study included 2705 patients with breast cancer detected by the Welsh breast cancer-screening programme from its inception in 1989 to 1997. Survival was tracked until 1999. Data validity was assessed for 10% of subjects. Hospitals' and surgeons' annual patient volumes were calculated as indices of specialisation. Effects of hospital and surgeon volumes on survival were estimated using Cox regression. Surgeons' and hospitals' volumes ranged from 1 to 90, and 1 to 86 patients, respectively. Patients managed by higher volume surgeons survived significantly longer (adjusted hazards ratio for a volume difference of 10 patients per year=0.90 (95% confidence intervals 0.84-0.97)). The adjusted hazard ratio for breast cancer survival was similar (0.91 (95% confidence intervals 0.82-1.00)). This association decreased over time. Patients of higher volume surgeons were significantly more likely to have axillary surgery and impalpable excision biopsies and were less likely to have mastectomy or radiotherapy. Surgeons' specialisation in management of screen-detected breast cancers was associated with longer survival, but this effect appeared to decrease over time.