Background: Tobacco use remains a major preventable cause of cancer in Low- and Middle-Income Countries (LMICs), particularly in India, where bidis, cigarettes, and diverse smokeless tobacco products coexist. Despite extensive tobacco control legislation, bidis remain weakly regulated and widely consumed. Evidence comparing the carcinogenic risk of bidis relative to other tobacco products, as well as their association with disease severity and treatment burden, remains limited. Addressing these gaps is critical for targeted cancer prevention and tobacco regulation in LMIC settings.

Objectives: To quantify and compare the association of bidi smoking with cancer risk, metastatic presentation at diagnosis, and treatment intensity, relative to cigarettes, smokeless tobacco, and dual/poly-tobacco use, in a multi-regional Indian population.

Methods: A multi-centre hospital-based case–control study was conducted across seven Indian states, involving 2,037 cancer cases and 2,066 cancer-free controls. Detailed tobacco-use histories, sociodemographic variables, and clinical data were collected using a standardized, validated questionnaire by trained local investigators, contributing to regional research capacity building. Covariate imbalance was assessed using standardized differences. Cancer occurrence and metastatic presentation were analysed using Firth-penalized binary logistic regression, while treatment intensity was examined using proportional-odds ordinal logistic regression. All models were adjusted for age, sex, education, occupation, income, diet, alcohol use, Asian BMI category, hypertension, diabetes, and religion.

Results: Exclusive bidi smoking was associated with the highest cancer risk among single-product users (adjusted odds ratio [aOR] 4.52; 95% CI 2.85–7.16), exceeding risks from exclusive cigarette smoking (aOR 3.87; 95% CI 1.90–7.91) and smokeless tobacco use (aOR 2.21; 95% CI 1.81–2.71). Dual bidi–cigarette use demonstrated a markedly elevated risk (aOR 10.05; 95% CI 2.75–36.73). Clear dose–response relationships were observed for bidi smoking duration (≥10 years: aOR 6.00; 95% CI 4.02–8.95) and daily consumption (≥10 bidis/day: aOR 5.35; 95% CI 3.50–8.17). Bidi and poly-tobacco use were also independently associated with higher odds of metastatic disease at diagnosis (exclusive bidi use: aOR 2.08) and increased treatment intensity (exclusive bidi use: aOR 1.54).

Conclusions/Implications: Bidi smoking confers a disproportionately high risk of cancer, advanced disease presentation, and greater treatment burden compared with other tobacco products in India. The pronounced risks associated with dual and poly-tobacco use underscore the need for regulatory parity, targeted cessation strategies, and strengthened surveillance of bidi consumption. These findings provide robust, policy-relevant evidence to inform tobacco control and cancer prevention strategies in LMICs.