Calculated cancer risks for conventional and "potentially reduced exposure product" cigarettes

Toxicant deliveries (by machine smoking) are compiled and associated cancer risks are calculated for 13 carcinogens from 26 brands of conventional cigarettes categorized as "regular" (R), "light" (Lt), or "ultralight" (ULt), and for a reference cigarette. Eight "potentially reduced exposure product" (PREP) cigarettes are also considered. Because agency-to-agency differences exist in the cancer slope factor (CSF) values adopted for some carcinogens, two CSF sets were used in the calculations: set I [U.S. Environmental Protection Agency (EPA)-accepted values plus California EPA-accepted values as needed to fill data gaps] and set II (vice versa). The potential effects of human smoking patterns on cigarette deliveries are considered. Acetaldehyde, 1,3-butadiene, and acrylonitrile are associated with the largest calculated cancer risks for all 26 brands of conventional cigarettes. The calculated risks are proportional to the smoking dose z (pack-years). Using CSF set I and z = 1 pack-year (7,300 cigarettes), the calculated brand-average incremental lifetime cancer risk ILCR₁ ^acetaldehyde values are R, 6 × 10^-5; Lt, 5 × 10^-5; and ULt, 3 × 10^-5 (cf. typical U.S. EPA risk benchmark of 10^-6). These values are similar, especially given the tendency of smokers to "compensate" when smoking Lt and ULt cigarettes. ILCR₁^subΣ-lung is the brand-average per pack-year subtotal risk for the measured human lung carcinogens. Using CSF set I, the ILCR₁^subΣ-lung values for R, Lt, and ULt cigarettes account for ≤2% of epidemiologically observed values of the all-smoker population average per pack-year risk of lung cancer from conventional cigarettes. R_PREP (%) is a science-based estimate of the possible reduction in lung cancer risk provided by a particular PREP as compared with conventional cigarettes. Using CSF set I, all R_PREP values are <2%. The current inability to account for the observed health risks of smoking based on existing data indicates that current expressed/implied marketing promises of reduced harm from PREPs are unverified: there is little reason to be confident that total removal of the currently measured human lung carcinogens would reduce the incidence of lung cancer among smokers by any noticeable amount.