Association between body mass index and localization of breast cancer: results from a nationwide inpatient database in Japan.

PURPOSE: Although both localization of breast cancer and body mass index (BMI) are associated with prognosis, the association between localization of breast cancer and BMI remains unclear. This study aimed to investigate the association between localization of breast cancer and BMI at diagnosis.

METHODS

Patients who underwent surgery for stage 0-III breast cancer July 2010-March 2017 were identified retrospectively in a Japanese nationwide inpatient database. Multinomial logistic regression analyses adjusting for patient's age were conducted to compare the outcomes among five BMI groups: < 18.5 kg/m2 (n = 31,724; 9.3%), 18.5-24.9 kg/m2 (n = 218,244; 64.3%), 25.0-29.9 kg/m2 (n = 69,813; 20.6%), 30.0-34.9 kg/m2 (n = 16,052; 4.7%), and ≥ 35.0 kg/m2 (n = 3716; 1.1%). The outcomes were the quadrant and side of the breast where tumors were detected.

RESULTS

In total, about half of the patients had breast cancer in the upper-outer quadrant (49.7%) and in the left breast (51.1%). In the multinomial analysis, BMI ≥ 25.0 kg/m2 was associated with the occurrence of breast cancer in the upper-inner and lower-outer quadrants and in the central area, whereas BMI < 18.5 kg/m2 was associated with the occurrence of breast cancer in the central area only. The side of breast cancer did not differ significantly among the five BMI groups.

CONCLUSIONS

Localization of breast cancer was associated with BMI in this large nationwide cohort. The findings may benefit patients' self-checks and doctors' examinations, potentially resulting in early detection and treatment.