Incidence of smoking-related cancers--excluding lung cancer--dropped rapidly after people in the D:A:D study group stopped smoking . Although lung cancer incidence falls in the general population when people quit smoking , it remained elevated for several years after cessation in this HIV group. [ 10 years after quitting: The lung cancer death rate is about half that of a person who is still smoking. (US Surgeon General's Report, 2010 see link below)
As HIV populations live longer with antiretroviral therapy, they face a growing risk of age-related cancers. Because smoking remains more prevalent in people with HIV than in the general population, smoking-related cancers pose a particular threat. Research has found declining cancer incidence in the general population after people stop smoking . D:A:D investigators conducted this study to assess the impact of smoking cessation on cancer incidence in people with HIV.
The analysis included all D:A:D participants who had no cancer history when they entered the study. The researchers set the baseline as the date of study entry or January 1, 2004. Follow-up continued until the first cancer diagnosis, death, the last visit plus 6 months, or February 1, 2015. They divided participants into four smoking categories: current smoker, never smoker, ex-smoker at baseline, and ex-smoker during follow-up (for less than 1 year, 1 to 2 years, 2 to 3 years, 3 to 5 years, or more than 5 years). To assess the impact of smoking cessation on cancer incidence, the researchers used Poisson regression models adjusted for age, gender, race, body mass index, calendar year, CD4 count, viral load, antiretroviral use, and several other variables.
The study group included 35,424 people, 72.5% men, with a median baseline age of 40 years and a median baseline CD4 count of 444. Just over half, 52.7%, had a baseline viral load below 500 copies. At baseline 46% of participants were smokers, 31% never-smokers, and 20% ex-smokers, while 4% had an unknown smoking status. Through a median 9 years of follow-up, the D:A:D team recorded 1980 new cancers, including 242 lung cancers, 487 smoking-related cancers excluding lung cancer, and 1251 smoking-unrelated cancers.
Incidence of all cancers fell steadily with increasing time since smoking stopped, from about 10 per 1000 person-years with less than 1 year since stopping to about 6 per 1000 with more than 5 years (P < 0.01). Incidence of smoking-unrelated cancers also fell significantly with longer time since cessation (P < 0.01), as did incidence of smoking-related cancers excluding lung cancer (from about 3.5 per 1000 person-years to about 1.5, P = 0.05). Lung cancer incidence declined nonsignificantly with longer time since cessation (P = 0.14). Adjusted rate ratios comparing each of the five cessation durations with never smoking also found significant trends for lower incidence with longer cessation for all cancers (P < 0.01), smoking-unrelated cancers (P = 0.04), and smoking-related cancers excluding lung cancer (P = 0.04), but not for lung cancer (P = 0.13).
The D:A:D investigators speculated that lung cancer incidence remains elevated longer after smoking stops because "the oncogenic potential for smoking is not reversed for lung cancer in the time frame that we have investigated." They note that this finding contrasts with results of similar studies in the general population , which trace a steady ebb in lung cancer incidence with longer time since smoking cessation. In the D:A:D study, incidence of smoking-related cancers other than lung cancer fell rapidly after smoking stopped.
The D:A:D team stressed that "deterring uptake of smoking and smoking cessation efforts should be a priority to reduce the risk of cancer" in people with HIV. They recommend continuing surveillance and awareness of lung cancer in people who stop smoking.
- Shepherd L, Ryom L, Petoumenos K, et al. Cessation of cigarette smoking and the impact on cancer incidence in the D:A:D study. Conference on Retroviruses and Opportunistic Infections (CROI), February 13-16, 2017, Seattle. Abstract 131.
- Oncolink. Abramson Cancer Center of the University of Pennsylvania. Former smokers and cancer risk. https://www.oncolink.org/risk-and-prevention/smoking-tobacco-and-cancer/former-smokers-and-cancer-risk
- Fry JS, Lee PN, Forey BA, Coombs KJ. How rapidly does the excess risk of lung cancer decline following quitting smoking? A quantitative review using the negative exponential model. Regulatory Toxicology and Pharmacology. 2013;67:13-26. http://www.sciencedirect.com/science/article/pii/S0273230013000871