# Association of Chewing Tobacco and the Risk of Breast Cancer in Indian Women: A Multicentre Case‐Control Study

## TL;DR

This study finds that chewing tobacco increases breast cancer risk in Indian women, especially with long-term use or early initiation.

## Contribution

The study is one of the first to show a link between chewing tobacco and all breast cancer subtypes in Indian women.

## Key findings

- Chewing tobacco increases breast cancer risk (OR: 1.19) across all subtypes.
- Longer duration of chewing (over 25 years) raises risk (OR: 1.38).
- Early initiation (<20 years) before first pregnancy increases risk further.

## Abstract

Even though breast cancer (BC) is the most common female cancer worldwide, the role of tobacco, specifically chewing tobacco in the development of BC has not been widely studied. This study is aimed at assessing this association.

A multicentre hospital‐based case‐control study was utilised. Two thousand five hundred fifty‐three histopathologically confirmed BC cases, and 2239 visitor controls were included. Self‐reported information was collected regarding tobacco consumption and other potential confounders. A logistic regression model was used to calculate odds ratio (OR) and its 95% confidence interval (CI), after adjusting for age, current residential region, education, various reproductive factors, BMI and history of benign breast lump. Attributable fraction (AF) and population attributable fraction (PAF) of BC due to chewing tobacco were also calculated.

An increased risk of BC was observed in women who ever used chewing tobacco (OR:1.19, 95% CI:1.00‐1.41) as compared to those who never consumed tobacco (smoking and chewing), consistent across all subtypes of BC. A dose‐response relation was observed for duration of tobacco chewing (OR>25 years: 1.38, 95% CI: 1.04–1.83). Women who initiated chewing tobacco at < 20 years, before their first full‐term pregnancy (FFTP), had more risk. Observed association was consistent even after stratification on menopausal status. The AF of BC due to tobacco chewing in our study was calculated to be approximately 3%, whereas the PAF for India was about 2%.

Our study suggests that chewing tobacco is associated with an increased risk of BC for all subtypes. This is particularly true when the duration of exposure is higher and exposure begins before FFTP. This highlights the need to target tobacco control policies to smokeless tobacco along with smoking, thus reducing the burden of BC to some extent.