Association of Body Mass Index With 21-Gene Recurrence Score Among Women With Estrogen Receptor-Positive, ERBB2-Negative Breast Cancer

Abstract

IMPORTANCE Body mass index (BMI) may affect the 21-gene recurrence score (RS) in patients with ER-positive, ERBB2-negative breast cancer. If high BMI increases genomic risk in ER-positive, ERBB2-negative breast cancer, weight control will become more important. OBJECTIVE To assess the association between RS and BMI according to age groups and address BM I as a factor associated with high RS. DESIGN, SETTING, AND PARTICIPANTS This cohort study included 2295 patients with ER-positive, ERBB2-negative breast cancer who had undergone a multigene assay between March 29, 2010, and December 31, 2020, in 2 hospitals. All of the study patients were Korean women, and the median follow-up period was 45 months (range, 1-40 months). The correlations between continuous RS and BM I were investigated. A high BMI was defined as a body mass index greater than or equal to 25. In the younger age group (age <= 45 years), a high RS was defined as an RS of greater than 20. EXPOSURES Body mass index. MAIN OUTCOMES AND MEASURES The Pearson correlation coefficient was used to estimate the association between RS and BMI. A multivariable binary logistic model was used to identify high RS. RESULTS Among the 2295 women included (mean [SD] age, 49.8 [4.00] years; range, 22-81years), 776 were aged 45 years or younger; RS and BMI were weakly correlated (correlation coefficient, 0.119; P < .001) in this younger group. Among them, the proportion of patients with an RS greater than 20 was significantly higher in the high BMI group than in the normal BMI group (45.5% [46 of 101] vs 27.3% [184 of 675]; P < .001). In the multivariable analysis, high BMI was an associated factor for high RS (odds ratio, 2.06; 95% CI, 1.28-3.32; P = .003). The 21-gene multigene assay-guided chemotherapy rate was significantly higher in patients with high BMI (30.7% [31of 101] vs 20.2% [136 of 674]; P = .02). CONCLUSIONS AND RELEVANCE In this cohort study of women aged 45 years or younger, high BMI was associated with higher RS in those with ER-positive, ERBB2-negative breast cancer; further studies are necessary to examine the underlying mechanisms.