Obesity and Early-Onset Breast Cancer and Specific Molecular Subtype Diagnosis in Black and White Women

Importance Epidemiologic data suggest an association of obesity with breast cancer (BC); however, obesity’s contribution to early onset and risk of diagnosis with specific molecular subtypes by race is uncertain. Objective To examine the race-specific association of body mass index with early onset and diagnosis of specific molecular subtypes. Design, Setting, and Participants This retrospective cohort study included patients with BC diagnosed between October 1, 2017, and March 31, 2022, at 3 University of South Alabama Mitchell Cancer Institute clinics. Participants were also prospectively enrolled for serum leptin measurement. Main Outcomes and Measures The primary outcome was age at BC onset and specific subtype diagnosis. The secondary outcome was race-specific differences. Odds ratios (ORs) for associations of body mass index with age at onset and subtype were estimated using the Fisher exact test. Race was self-reported. Results Of the 1085 study patients, 332 (30.6%) were Black with a median age of 58 (IQR, 50-66) years, and 753 (69.4%) were White with a median age of 63 (IQR, 53-71) years. A total of 499 patients (46.0%) had obesity, with Black women with obesity receiving more frequent BC diagnosis than their White counterparts (OR, 2.40; 95% CI, 1.87-3.15; P lt; .001). In addition, Black women had a significantly higher incidence of early-onset disease (OR, 1.95; 95% CI, 1.33-2.86; P = .001) than White women, and obesity increased this risk significantly in Black women (OR, 2.92; 95% CI, 1.35-6.22; P = .006). Black women with obesity also had a significantly higher risk of luminal A BC (OR, 2.53; 95% CI, 1.81-3.56; P lt; .001) and triple-negative BC (TNBC) (OR, 2.48; 95% CI, 1.43-4.22; P = .002) diagnosis than White counterparts. Black women, with or without BC, had significantly higher serum leptin levels (median IQR, 55.3 40.3-66.2 ng/mL and 29.1 21.1-46.5 ng/mL, respectively, P lt; .001) than White women (median IQR, 33.4 18.9-47.7 ng/mL and 16.5 10.0-22.9 ng/mL, respectively), which was associated with higher odds of luminal A disease (OR, 5.25; 95% CI, 1.69-14.32, P = .003). Higher odds of early-onset disease (OR, 3.50; 95% CI, 0.43-23.15; P = .33 for trend), and TNBC diagnosis (OR, 6.00; 95% CI, 0.83-37.27; P = .14 for trend) were also seen, although these outcomes were not statistically significant. Conclusions and Relevance In this cohort study of patients with BC, obesity and high serum leptin levels were associated with an enhanced risk of early-onset BC and diagnosis of luminal A and TNBC subtypes in Black women. These findings should help in developing strategies to narrow the existing disparity gaps.