Reexamining the Relationship of Breast Cancer Hospital and Surgical Volume to Mortality: An Instrumental Variable Analysis

Abstract

Objective: To reexamine the relationship of hospital and surgical volume to all-cause and breast cancer-specific mortality, taking into account the potential selection bias in patients treated at high-volume centers or by high-volume surgeons.

Data sources: Elderly (65+) women with early-stage, incident breast cancer surgery in 2003.

Study design: A population-based, prospective survey study.

Methods: Two-stage, instrumental variable regression models.

Principal findings: Women treated in high-volume hospitals were significantly less likely to die of any cause by 5 years after surgery, even after adjustments for self-selection and a number of other factors. The relationship was larger and more significant for breast cancer-specific mortality. Although the general pattern of better mortality outcomes held for moderately sized hospitals, the relationships were not statistically significant. In contrast, there was no relationship of surgeon volume with all-cause or breast cancer-specific mortality.

Conclusions: Hospital volume, but not surgeon volume, is associated with better survival among women with breast cancer. The magnitude of the potential improvement was substantial and comparable with the benefit conferred by many systemic therapies. These findings highlight the importance of accounting for patient self-selection in volume-outcome analyses, and provide support for policy initiatives aimed at regionalizing breast cancer care in the United States.

Figure 1

High breast cancer volume hospitals and their associated 100-mile driving distances.