Importance: California's tobacco control efforts have been associated with a decrease in cancer mortality, but these estimates are based on smoking prevalence of the general population. Patient-level tobacco use information allows for more precise estimates of the proportion of cancer deaths attributable to smoking.
Objective: To calculate the proportion (smoking-attributable fraction) and number (smoking-attributable cancer mortality) of cancer deaths attributable to tobacco use using patient-level data.
Design, setting, and participants: The smoking-attributable fraction and smoking-attributable cancer mortality were calculated for a retrospective cohort of patients whose cancer was diagnosed from 2014 to 2019 with at least 1 year of follow-up using relative risks from large US prospective studies and patient-level smoking information. Follow-up continued through April 2022. A population-based cohort was identified from the California Cancer Registry. Participants included adults aged 20 years and older with a diagnosis of 1 of the 12 tobacco-related cancers (oral cavity or pharynx, larynx, esophagus, lung, liver, stomach, pancreas, kidney, bladder, colon or rectum, cervix, and acute myeloid leukemia).
Exposures: Tobacco use defined as current, former, or never.
Main outcomes and measures: The primary outcomes were the smoking-attributable fraction and smoking-attributable cancer mortality for each of the 12 tobacco-related cancers over 2 time periods (2014-2016 vs 2017-2019) and by sex.
Results: Among 395 459 patients with a tobacco-related cancer, most (285 768 patients [72.3%]) were older than 60 years, the majority (228 054 patients [57.7%]) were non-Hispanic White, 229 188 patients were men (58.0%), and nearly one-half (184 415 patients [46.6%]) had lung or colorectal cancers. Nearly one-half of the deaths (93 764 patients [45.8%]) in the cohort were attributable to tobacco. More than one-half (227 660 patients [57.6%]) of patients had ever used tobacco, and 69 103 patients (17.5%) were current tobacco users, which was higher than the proportion in the general population (11.7%). The overall smoking-attributable fraction of cancer deaths decreased significantly from 47.7% (95% CI, 47.3%-48.0%) in 2014 to 2016 to 44.8% (95% CI, 44.5%-45.1%) in 2017 to 2019, and this decrease was seen for both men and women. The overall smoking-attributable cancer mortality decreased by 10.2%.
Conclusions and relevance: California still has a substantial burden of tobacco use and associated cancer. The proportion of cancer deaths associated with tobacco use was almost double what was previously estimated. There was a modest but significant decline in this proportion for overall tobacco-associated cancers, especially for women.