OBJECTIVES: Lynch syndrome (LS), occurring in about 1 in 279 people, is among the most common hereditary cancer syndromes. LS is associated with increased risk of a variety of cancers, including colorectal, endometrial, ovarian, stomach, urinary tract, and pancreatic, among others. Some studies suggest that breast cancer should be included as an LS-linked cancer, but definitive evidence is lacking. The objective of this study was to use administrative claims data to determine the statistical strength of association of LS with breast cancer.

METHODS: A retrospective analysis of U.S. claims data (2015-2022) was conducted using Merative™ MarketScan® Treatment Pathways. Prevalence of breast cancer (ICD-9/ICD-10 diagnoses) was compared between patients with tests (CPT codes) and diagnoses (ICD-9/ICD-10) indicating probable LS and patients without LS. Patients with diagnoses indicating genetic susceptibility to breast cancer specifically (e.g., BRCA1, BRCA2 mutations) were excluded. Strength of association between LS and breast cancer was evaluated using odds ratios (OR) with 95% confidence intervals (95%CI).

RESULTS: We identified 1,564 patients tested and diagnosed with LS (“LS Cohort”) and 5,262,738 patients without LS (“Control Cohort”). Large differences in breast cancer prevalence were found between cohorts, corresponding with significantly (p<0.0001) strong association between LS and all breast cancer types examined. Prevalence of “any breast cancer” in the LS Cohort was 6.97% versus 0.76% in the Control Cohort (OR = 9.72, 95%CI [8.00, 11.81]). Statistically significant results for association were also found the malignant and in situ breast cancer subtypes.

CONCLUSIONS: This study demonstrates the value and power of using retrospective claims data for conducting exploratory epidemiology studies in diseases that are not well understood. Analysis results indicate that there is a significantly strong association of LS with breast cancer. These findings suggest that women diagnosed with LS may benefit from increased and more targeted breast cancer screening.