Relationship between number of breast cancer operations performed and 5-year survival after treatment for early-stage breast cancer

Abstract

Objectives: We examined the association between number of breast cancer operations performed in a hospital (hospital volume) and all-cause and breast cancer-specific mortality using a national database and statistical methods appropriate for clustering and reducing confounding.

Methods: In a retrospective cohort study, we linked Surveillance, Epidemiology, and End Results tumor registry data with Medicare claims data. The cohort included 11225 Medicare patients who had undergone surgery for early-stage breast cancer from 1994 to 1996 in 457 different hospitals. Primary outcomes were all-cause and breast cancer-specific survival rates at a mean follow-up time of 62.5 months.

Results: In comparison with treatment in a low-volume hospital, treatment in a high-volume hospital was associated with hazard ratios of 0.83 (95% confidence interval [CI]=0.75, 0.92) for all-cause mortality and 0.80 (CI=0.66, 0.97) for breast cancer-specific mortality.

Conclusions: An association between the volume of breast cancer operations performed in a hospital and 5-year survival rates was observed for both all-cause and breast cancer-specific mortality. Further work investigating the aspects of hospital volume that contribute to increased survival is warranted.

FIGURE 1—

Unadjusted all-cause mortality survival curve, by annual hospital volume^a of Medicare breast cancer cases: United States, 1994–1996. ^aLow volume = 0–19 operations performed per year; medium volume = 20–39 operations performed per year; and high volume = 40 or more operations performed per year.

FIGURE 2—

Adjusted all-cause mortality survival curve, by annual hospital volume^a of Medicare breast cancer cases: United States, 1994–1996. Note. Shown are survival curves constructed for 2 patient profiles differing only in their lymph node status (positive [bottom 3 lines] or negative [top 3 lines]). Covariates that were held constant for the 2 profiles included age (70 years), race (White), area or residence (urban), comorbidity index value (0), tumor size (less than 20 mm), estrogen receptor/progesterone receptor positive, tumor grade (1 or 2), per capita income (less than $15 008), and propensity group (midlevel). ^aLow volume =0–19 operations performed per year; medium volume = 20–39 operations performed per year; and high volume = 40 or more operations performed per year.