# Association between body mass index and risk of breast cancer according to breast cancer subtypes: A systematic review and meta-analysis

## TL;DR

Higher BMI increases the risk of ER-positive breast cancer, especially in postmenopausal women, while effects differ by menopausal status and cancer subtype.

## Contribution

This study clarifies how BMI affects breast cancer risk by subtype and menopausal status through a systematic review and meta-analysis.

## Key findings

- Obesity is linked to a moderate increased risk of ER-positive breast cancer.
- Premenopausal overweight is associated with lower ER-positive but higher ER-negative and TNBC risk.
- Postmenopausal obesity shows a stronger association with ER-positive breast cancer.

## Abstract

Higher body mass index (BMI) is a risk factor for breast cancer (BC) development, but the relationship with BC subtypes in pre- and post-menopausal women remains unclear.

We performed a systematic search from PubMed, Embase and Cochrane databases until 09/24 (CRD42020206108) for cohort and case-control studies assessing the association between BMI and BC subtypes and/or menopausal status. BC risk in overweight (BMI 25–29.9 kg/m2) or obese (BMI≥30 kg/m2) subjects was compared to risk in under/normal weight (BMI<25 kg/m2). BC subtypes were classified as i) ER-positive (regardless HER2-status) ii) ER-negative (regardless HER2-status) iii) HER2-positive (regardless ER-status); iv) triple-negative BC (TNBC).

Out of 2841 records screened, 33 studies (9 cohort and 24 case-control) including 2,103,181 women were eligible. Obesity was associated with a modestly increased risk of ER-positive BC (pOR 1.13; 95 % CI 1.03–1.24). In postmenopausal women, obesity was associated with a moderate higher risk of ER-positive BC (pOR 1.29; 95 % CI 1.18–1.41), while overweight was associated with an increased risk of ER-positive (pOR 1.14; 95 % CI 1.06–1.22) and HER2-positive BC (pOR 1.13; 95 % CI 1.05–1.22). In premenopausal women, overweight was linked with reduced risk of ER-positive (pOR 0.80 95 % CI 0.71–0.91) but increased risk of ER-negative BC (pOR 1.15 95 % CI 1.05–1.26) and TNBC (pOR 1.30; 95 % CI 1.15–1.47).

Obesity was associated with a modestly higher risk of ER-positive BC, driven by postmenopausal status. Considering potential confounders, in premenopausal women, higher BMI was associated with lower risk of ER-positive BC, and an increased risk of ER-negative BC.

•Obesity is associated with a moderate increased risk of ER-positive BC.•The risk of BC by BMI differs according to menopausal status•Postmenopausal obesity shows stronger association with ER-positive BC•Further studies are needed to assess BMI-related breast cancer risk.

Obesity is associated with a moderate increased risk of ER-positive BC.

The risk of BC by BMI differs according to menopausal status

Postmenopausal obesity shows stronger association with ER-positive BC

Further studies are needed to assess BMI-related breast cancer risk.