Prior Pneumonia, Smoking, and Drinking Explain Higher Lung Cancer Risk With HIV

A past pneumonia episode largely explained a higher risk of lung cancer in people living with HIV, according to a large study in California. The study, which was published in the journal AIDS, followed nearly 300,000 people of mixed HIV status, and found that factors like smoking and drug or alcohol abuse also contributed to a higher lung cancer risk in people living with HIV, but a recent low CD4 count did not.

People living with HIV run a higher risk of several cancers including lung cancer than people the same age without HIV. The greater lung cancer risk can be partly traced to higher smoking rates in people with HIV. But statistical methods that calculate the impact of smoking on lung cancer still find a higher lung cancer risk in people with HIV than their HIV-negative counterparts. U.S. researchers conducted this study to examine other factors that may make lung cancer more likely with HIV, including low CD4 counts with HIV and previous pneumonia.

The study involved HIV-positive and negative people in a large California health care system. For every HIV-positive person, the researchers selected 10 HIV-negative people matched for sex (male or female), age, medical center, and first year in the health care system. The researchers used medical records to collect relevant personal and health data and to find people with a new lung cancer diagnosis during the 1996-2011 study period. The investigators then calculated differences in lung cancer rates between the HIV-positive and negative groups after statistical adjustment for several lung cancer risk factors, allowing them to isolate risk factors that contributed most to lung cancer.

The researchers checked lung cancer rates in 24,768 people living with HIV and 257,600 people without HIV. Follow-up time averaged 4.9 years in the HIV group, compared to 5.8 years. Age averaged about 40 years in both groups, and about 90% of participants were men. Higher proportions of people with HIV were white (56.2% versus 44.1%) or black (17.8% versus 10.4%) and lower proportions were Hispanic or members of other racial/ethnic groups. A significantly higher proportion of people with HIV smoked (45.2% versus 31.1%) or abused drugs or alcohol (20.6% versus 8.6%).

Overall lung cancer rate was twice as high in people with HIV (66 versus 33 per 100,000 person-years, meaning 66 of every 100,000 people with HIV got lung cancer in each study year). Further analysis determined that people with HIV faced a lung cancer rate almost double what people without HIV did even after statistical adjustment for the impact of factors like age, sex and race (rate ratio 1.9). And after adjustment for the impact of smoking, drug or alcohol abuse, and obesity, people with HIV still had a 40% higher lung cancer rate (rate ratio 1.4). But after additional statistical adjustment for prior pneumonia, the new lung cancer rate was no longer significantly higher in people with HIV infection.

The researchers then performed similar analyses to estimate the impact of recent CD4 count between 200 and 499 cells/mm3 or below 200 cells/mm3 on lung cancer risk. These calculations determined that, unlike prior pneumonia, recent low CD4 count did not contribute to a higher lung cancer risk for people living with HIV.

This study confirms that well-known lung cancer risk factors -- including smoking and drug or alcohol abuse -- contribute to higher rates of lung cancer in people with HIV. Also, a previous pneumonia episode had a large impact on lung cancer risk, a result reflecting previous research in women and men with HIV. These findings underline the importance of lung cancer screening, smoke-ending programs, and pneumococcal vaccination in people living with HIV.