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Smoking explains 1 in 5 cancers in people with HIV--and almost all lung cancers.

Smoking explained 19% of all new cancers in a study of 52,441 North Americans with HIV. (1) Smoking accounted for 50% of all new smoking-related cancers and 94% of all lung cancers. In other words, almost 20% of all new cancers, half of all smoking-related cancers and almost all lung cancers could be prevented in people with HIV if they did not smoke.

As people live longer with HIV thanks to antiretroviral therapy,* cancer has become an increasingly important cause of sickness and death. (2,3) Smoking causes or contributes to many cancers, not just lung cancer. A combined analysis of 113 studies, mostly in North America and Western Europe, found that 54% of people with HIV currently smoke. (4) A nationwide US study determined that 42% of people with HIV smoke, compared with 21% of the general population. (5)

A study of HIV-positive people in Denmark figured that smoking causes 27% of all cancers and 91% of smoking-related cancers. (6) Researchers conducted a new study to figure proportions of cancers that can be attributed to smoking among people with HIV in the United States and Canada. (1)

How the study worked.

Study participants

came from NA-ACCORD, a collection of 22 study groups of HIV-positive adults in care across the United States and Canada. This analysis included 16 study groups with data on cancer and smoking. All the people analyzed were free from cancer when they entered this study. Everyone was taking antiretroviral therapy.

Researchers determined how many of these people had a new cancer from 2000 through 2015. They identified new diagnoses of all cancers, smoking-related cancers, and lung cancer. Smoking-related cancers were cancers of the lung, liver, colon and rectum, oral cavity, kidney, cervix, bladder, larynx, pancreas, esophagus, stomach, and leukemia.

The research team used accepted statistical methods to determine the impact of smoking on development of all cancers, smoking-related cancers, and lung cancer. This kind of analysis can determine whether smoking by itself contributes to development of these cancers, regardless of any other cancer risk factors a person may have. They also used standard methods to determine population-attributable fraction (PAF). In this study PAF describes the proportion of new cancers that can be attributed to smoking. The World Health Organization explains PAF as "the proportional reduction in population disease or mortality that would occur if exposure to a risk factor were reduced to an alternative ideal exposure scenario," for example, tobacco use versus no tobacco use. (7)

What the study found.

The analysis included 52,441 HIV-positive adults with a median (midpoint) observation time 3.8 years. Most study participants, 78%, were men, and 51% were 40 years old or older. About three quarters of participants, 73%, ever smoked, while 27% never smoked.

During the observation period, cancer developed in 2306 people (4.4%) to yield an incidence of 8.5 per 1000 person-years, meaning providers found a new cancer in 8 or 9 of every 1000 people every year. While 79% of people in whom a cancer developed ever smoked, 73% of people who remained free of cancer ever smoked. This difference is statistically significant, meaning a statistical test shows there is only a small possibility that chance explains the difference.

People with cancer detected during the study period were older and more likely to be men than women (81% versus 78%). These differences were also statistically significant. While 30% of people with a new cancer had a CD4 count below 200 when they entered the study period, 24% without a new cancer had a CD4 count that low--another statistically significant difference between the two groups.

Statistical analysis that considers several cancer risk factors at the same time determined that smoking alone raised chances of all cancers, smoking-related cancers, lung cancers, and smoking-related cancers excluding lung cancer:

Smoking raised risk of these types of cancer:

* All cancers combined: raised risk 1.33 times

* Smoking-related cancers: raised risk 2.31 times

* All smoking-related cancers except lung cancer: raised risk 1.59 times

* Lung cancer: raised risk 17.8 times

Smoking alone did not raise chances of cancers not related to smoking.

The population-attributable fraction analysis determined that 19% of all cancers could be attributed to ever smoking; 50% of smoking-related cancers could be attributed to ever smoking; and 94% of lung cancers could be attributed to ever smoking (Figure 1). In other words, if these people with HIV never smoked, they would avoid 19% of all cancers, 50% of all smoking-related cancers, and almost all lung cancers--94%.

What the findings mean for you. This well planned analysis of US and Canadian adults being treated for HIV confirms much previous research showing the devastating impact of smoking on cancer risk. Smoking causes or contributes not only to lung cancer, but also to cancer of the liver, colon, mouth, stomach, and other organs. (See "How the study worked" above.)

In this study smoking more than doubled the risk of smoking-related cancers and raised the risk of lung cancer almost 18 times. If people in this study group never smoked, they would avoid about 1 in 5 cancers of any kind and 50% of smoking-related cancers. Smoking also greatly raises the risk of potentially deadly noncancer lung disease, heart disease, and stroke.

Large studies show that 40% to 50% of people with HIV smoke. (4,5) Those rates double the smoking rate in people without HIV. If you don't smoke, don't start. It's the simplest thing you can do to live a longer and healthier life.

If you do smoke, meet with your HIV provider to make a plan to quit. Some people can make up their mind to quit and never touch another cigarette. For most people, quitting is harder, but it can be done. The United States has more people who quit smoking than who still smoke. (8) Smoking experts know that many people succeed at quitting only after several failed attempts. So if you tried and failed to quit smoking, don't give up. Keep trying.

Your HIV provider can help by deciding whether you're a good candidate for nicotine-replacement strategies or for smoke-ending medications like Chantix or Zyban. Researchers and people with HIV developed an online quitting program--Positively-SmokeFree--specifically for HIV-positive smokers. Go to the link at reference 9 below to work through the interactive Web-based sessions in private and at your own pace. For HIV providers, the US Department of Veterans Affairs has a useful online guide to smoking cessation. (10)


(1.) Altekruse SF, Shiels MS, Modur SP, et al. Cancer burden attributable to cigarette smoking among HIVinfected people in North America. AIDS. 2018;32:513-521.

(2.) Shiels MS, Pfeiffer RM, Gail MH, et al. Cancer burden in the HIV-infected population in the United States. J Natl Cancer Inst. 2011;103:753-762.

(3.) Weber R, Ruppik M, Rickenbach M, et al. Decreasing mortality and changing patterns of causes of death in the Swiss HIV Cohort Study. HIV Med. 2013;14:195-207.

(4.) Park LS, Hernandez-Ramirez RU, Silverberg MJ, Crothers K, Dubrow R. Prevalence of non-HIV cancer risk factors in persons living with HIV/AIDS: a meta-analysis. AIDS. 2016;30:273-291.

(5.) Mdodo R, Frazier EL, Dube SR, et al. Cigarette smoking prevalence among adults with HIV compared with the general adult population in the United States: cross-sectional surveys. Ann Intern Med. 2015;162:335-344.

(6.) Helleberg M, Gerstoft J, Afzal S, et al. Risk of cancer among HIV-infected individuals compared to the background population: impact of smoking and HIV. AIDS. 2014;28:1499-1508.

(7.) World Health Organization. Health statistics and information systems. Metrics: Population-attributable fraction (PAF). burden disease/metrics paf/en/

(8.) The Health Consequences of Smoking--50 Years of Progress: A Report of the Surgeon General. US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014.

(9.) PositivelySmokeFree.

(10.) U.S. Department of Veterans Affairs. Smoking cessation.

* Words in boldface are explained in the Technical Word List at the end of this issue.
Figure 1. Analysis of new cancers and smoking status
in 52,441 North Americans being treated for HIV
determined that cigarette smoking accounts for 19% of
all cancers, 50% of all smoking-related cancers, and 94%
of all lung cancers.

Cancers prevented by not smoking

All cancers        19%
Smoking related    50%
Lung cancer        94%

Proportion of cancers prevented

Note: Table made from bar graph.
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Title Annotation:ARTICLE 1
Publication:HIV Treatment: ALERTS!
Date:May 1, 2018
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