Facility Mammography Volume in Relation to Breast Cancer Screening Outcomes.

Objectives: To clarify the relationship between facility-level mammography interpretive volume and breast cancer screening outcomes. Methods: We calculated annual mammography interpretive volumes from 2000-2009 for 116 facilities participating in the U.S. Breast Cancer Surveillance Consortium (BCSC). Radiology, pathology, cancer registry, and women's self-report information were used to determine the indication for each exam, cancer characteristics, and patient characteristics. We examined the effect of annual total volume and percentage of mammograms that were screening on cancer detection rates using multinomial logistic regression adjusting for age, race/ethnicity, time since last mammogram, and BCSC registries. Good prognosis tumours were defined as screen-detected invasive cancers that were <15mm, early stage, and lymph node negative at diagnosis. Results: From 3,098,481 screening mammograms, 9,899 cancers were screen-detected within one year of the exam. Approximately 80% of facilities had annual total interpretive volumes of >2,000 mammograms, and 42% had >5,000. Higher total volume facilities were significantly more likely to diagnose invasive tumours with good prognoses (odds ratio [OR] 1.32; 95% confidence interval [CI] 1.10-1.60, for total volume of 5,000-10,000/year v. 1,000-2,000/year; p-for-trend <0.001). A concomitant decrease in tumours with poor prognosis was seen (OR 0.78; 95%CI 0.63-0.98 for total volume of 5,000-10,000/year v. 1,000-2,000/year). Conclusions: Mammography facilities with higher total interpretive volumes detected more good prognosis invasive tumours and fewer poor prognosis invasive tumours, suggesting that women attending these facilities may be more likely to benefit from screening.