Smokeless tobacco (snuff) and site‐specific cancer risks in adult Black South African women: Findings from the Johannesburg Cancer Study

Smokeless tobacco (SLT) use is an established carcinogen to the nasal cavity, lip, and oropharynx, however, few studies have examined cancer risks in older African women among whom SLT use is common. We investigated snuff use and the risk of site-specific cancers among 15,336 newly diagnosed female cancer patients in the Johannesburg Cancer Study, South Africa. We designed case-control comparisons across multiple cancer outcomes: (a) known SLT-associated cancers; (b) other tobacco-related cancers and (c) genital cancers owing to intravaginal snuff use. Controls (n = 2961) comprised all other cancer patients. We also investigated (d) each control cancer type versus the remaining controls to explore possible associations with other cancers. Logistic models were fitted to estimate odds ratios adjusted for age, education, tobacco smoking, alcohol, HIV, and language. Overall, ever use of snuff was 22% among control cancers. Ever snuff use was associated with cervical (OR 1.14 [95%CI 1.00-1.30]) and eye and adnexa cancer (OR 1.95 [95%CI 1.03-3.70]). Associations with vulva cancer were less clear, 95% CI's for the main effects included 1 but a subgroup analysis restricted to never-smokers of current-versus-never users was positive (OR 2.10 [95%CI 1.25-3.50]). Surprisingly SLT users have lower risks of stomach cancer (OR 0.60 [95%CI 0.37-0.99]) and Hodgkin Lymphoma (OR 0.48 [95%CI 0.23-0.97]). Snuff use may increase the risk for cervical and vulva cancer in women, which is plausible via intravaginal use. Further research on the impact of SLT on female genital cancers with more detailed exposure data, including timing, intensity, and routes of use are required.