Was breast conserving surgery underutilized for early stage breast cancer? Instrumental variables evidence for stage II patients from Iowa

Objective. To estimate the average survival effects of breast conserving surgery plus irradiation relative to mastectomy for marginal stage II breast cancer patients in Iowa from 1989-1994. Data Sources/Data Setting. Secondary linked Iowa SEER Cancer Registry-Iowa Hospital Association discharge abstract data for women in Iowa with stage II breast cancer from 1989-1994. Study Design. Observational instrumental variables (IV) analysis. Data Collection/Extraction Methods. Women with stage II breast cancer from the Iowa SEER Cancer Registry 1989-1994 who received all of their inpatient care in Iowa were linked with their respective hospital discharge abstracts. Principal Findings. Breast conserving surgery plus irradiation decreased survival relative to mastectomy for marginal stage II breast cancer patients in Iowa during the early 1990s. In this study marginal patients were those whose surgery choices were affected by differences in area treatment rates and access to radiation facilities. Conclusions. If marginal patients are representative of patients whose treatment choices would be affected by changes in treatment rates, an increase in the breast conserving surgery plus irradiation rate for stage II early stage breast cancer patients would have decreased survival in Iowa during the early 1990s. Further research with newer data and broader samples is needed to make more current and specific assessments.