Evaluation of Cancer Deaths Attributable to Tobacco in California, 2014-2019

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.To calculate the proportion (smoking-attributable fraction) and number (smoking-attributable cancer mortality) of cancer deaths attributable to tobacco use using patient-level data.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).Tobacco use defined as current, former, or never.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.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%.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.