People living with HIV on antiretroviral treatment with fully suppressed viral load who smoke are much more likely to die of lung cancer than HIV-related causes, according to the findings of a modelling study published today in JAMA Internal Medicine.
The study suggests that people on successful antiretroviral treatment are between six and thirteen times more likely to die of lung cancer than of any AIDS-related illness, and 10% of all people with HIV who are linked to care will eventually die of lung cancer.
The modelling study lends further weight to the view that smoking poses a greater threat to the health of people with well-controlled HIV disease than the virus itself.
Around 40% of people living with HIV in the United States are estimated to smoke compared to around 15% of the general population in 2015.
Smoking reduces life expectancy through cardiovascular disease (stroke and heart attack), cancers and chronic obstructive pulmonary disease (emphysema). A modelling study by the same research group estimated that in people with HIV with suppressed viral load on treatment, smoking cut life expectancy by six years.
Using data from recently published studies on people starting antiretroviral treatment in the United States, the researchers projected lung cancer mortality up to the age of 80 according to smoking behaviour and age at the start of HIV treatment. They also calculated the effects of stopping smoking at various ages on mortality.
The model assumed that people living with HIV entered care with a CD4 cell count of 360 cells/mm3, and that 87% of people who started treatment would achieve viral suppression. The researchers applied standard risks for developing lung cancer, derived from US general population data to current and former smokers. Smokers were stratified according to heavy (28 to 35 per day), moderate (14 to 18 per day) and light use (2 per day) at the age of 40. Smoking intensity was assumed to remain unchanged over time. Mortality risks were calculated by sex, age and smoking exposure.
Among men, cumulative lung cancer mortality by the age of 80 for heavy, moderate and light smokers who entered HIV care at the age of 40 and continued to smoke was 28.9%, 23% and 18.8%, respectively.
Stopping smoking had very substantial benefits. For heavy, moderate and light smokers who quit at age 40 cumulative mortality from lung cancer was 7.9%, 6.1% and 4.3%; and for people who never smoked it was 1.6%. Men who entered care at the age of 50 and stopped smoking also had a substantial reduction in mortality (13.5% for heavy smokers, 10.6% for moderate smokers and 7.7% for light smokers, compared to 1.6% for those who never smoked).
Among women, cumulative lung cancer mortality by the age of 80 for heavy, moderate and light smokers who entered HIV care at the age of 40 and continued to smoke was 27.8%, 20.9% and 16.6%, respectively; for heavy, moderate and light smokers who quit at age 40 it was 7.5%, 5.2% and 3.7%; and for women who never smoked it was 1.2%.
The model showed that male smokers who started HIV treatment at the age of 40 and adhered consistently to treatment were ten times more likely to die of lung cancer than an AIDS-related illness by the age of 80 (23 vs 2.3%). When all causes of mortality were considered, men aged 40 who smoked were 35 times more likely to die of lung cancer or another non-AIDS-related cause than of an AIDS-related cause and women 27 times more likely.
Just under 60,000 people living with HIV are likely to die of lung cancer by the age of 80 (9.3% of all people with HIV currently in care in the United States), the researchers estimate. The impact of smoking as a cause of death will become increasingly apparent as the population of people living with HIV ages, the study authors say. Lung cancer is already the leading cause of death among people with HIV in France, where levels of smoking are similar to those in the United States.
The study was carried out by Krishna P. Reddy, of the Massachusetts General Hospital, Boston, and colleagues.
The study authors recommend intensified efforts to help people with HIV stop smoking and for smoking cessation interventions to become a key component of the package of care for people with HIV, including pharmacologic treatments.
“Compared with arresting the replication of HIV, can it really be beyond our abilities to arrest the harms of tobacco?” asks Dr Mitchell Katz of Los Angeles County Department of Health in an accompanying comment article in JAMA Internal Medicine. He points out that doctors still under-prescribe nicotine replacement therapies such as varenicline and bupropion.
Reddy KP. Lung cancer mortality associated with smoking and smoking cessation among people living with HIV in the United States. JAMA Internal Medicine, advance online publication, 18 September 2017.
Katz M. If we are smart enough to stop HIV from replicating, why can’t we help people to stop smoking? JAMA Internal Medicine, advance online publication, 18 September 2017.