A protocol for three observational cohort studies evaluating adverse outcomes, excess costs and repeat procedures after surgery for breast cancer in the USA.

Surgical therapy for early-stage breast cancer, including lumpectomy and mastectomy, are common treatments for early-stage breast cancer. Despite having favorable survival outcomes, these procedures can lead to repeat surgeries, adverse outcomes, excess costs and potentially aggressive resections. This is a protocol for a study aims to evaluate three main areas: the risk factors, costs and complications of re-operations following lumpectomy ('Lumpectomy Cohort'), the identification of patients potentially overtreated with mastectomy ('Mastectomy Cohort') and the cost and healthcare resource utilization associated with nipple necrosis following nipple-sparing mastectomy (NSM) ('Nipple Necrosis Cohort'). A retrospective cohort analysis will be conducted using Optum's de-identified Market Clarity Data (2007-2023), which integrates medical and pharmacy claims with electronic health records. Patients will be included based on specific procedure and diagnosis codes, with additional data extracted from unstructured clinical notes using natural language processing. The study will analyze patient demographics, baseline health, surgical details, and outcomes, including costs, complications, reoperations and mortality. Data will be analyzed descriptively, with Kaplan-Meier analyses for time-to-event outcomes and Wilcoxon Signed Rank tests for cost comparisons. Preliminary cohorts are expected to include 26,472 lumpectomy patients, 16,836 mastectomy patients and 6828 NSM patients with 541 cases of nipple necrosis. This study will provide comprehensive insights into the patient journey - highlighting the costs and patient outcomes following lumpectomy, mastectomy and NSM - potentially guiding better clinical decision-making and resource allocation.