Smoking is sole risk for lung cancer for women with HIV

Cigarette smoking was the sole risk factor for the development of lung cancer in women with or at risk of HIV in a study published in the online edition of the Journal of Clinical Oncology.

The study also showed that incidence rates of lung cancer were similar between the HIV-positive and HIV-negative women. However, the lung cancer incidence in the study population was three times that seen in the general female US population. Once again, this could be explained by smoking habits, the researchers found.

“We found a substantially increased risk of lung cancer among both HIV-infected and at-risk uninfected women compared with population-based expectation. A possible explanation is the high rate of cigarette smoking”, write the investigators.

Rates of HIV-related cancers have fallen dramatically since effective antiretroviral therapy became available. However, this has been accompanied by an increase in the incidence of some non-AIDS-related cancers, including lung cancer.

This cancer is rare amongst people with HIV. Cigarette smoking has been identified as a strong risk factor, but some research suggests that prolonged duration of HIV infection may also play a role. However, the exact role of HIV-related factors remains unclear.

Because of these uncertainties, investigators from the Women’s Interagency HIV Study (WIHS) examined lung cancer rates in their cohort in the periods before and after effective multi-drug HIV treatment became available.

They compared the incidence of lung cancer between women with HIV and the study’s HIV-negative participants. Risk factors for the development of this cancer were also examined and compared between the HIV-positive and HIV-negative women.

A total of 3549 women, 898 of whom were HIV-negative, were followed over a twelve-year period between 1994 and 2006. The years 1994-1997 were defined as being the period before the availability of effective HIV treatment.

The women contributed a total of 25,000 person years of follow-up for analysis, with a median of 5.8 years per individual.

There were 14 incident lung cancers, twelve of which involved women with HIV. The overall incidence rate of lung cancer was 56 per 100,000 person years. This was similar for both the HIV-positive and HIV-negative women.

This incidence was three times that seen in age and race-matched women in the general population. This excess risk was similar for HIV-positive and HIV-negative women in the WIHS cohort, and for the eras before and after effective antiretroviral therapy became available.

Further analysis showed that both HIV-positive and HIV-negative women in the WIHS study were more likely to have a history of smoking than women in the general population (68% vs 37%, p < 0.001). Moreover, amongst current smokers, women in the WIHS study smoked approximately 50% more packs of cigarettes per year.

Next the investigators examined the risk factors for lung cancer for the women in their cohort.

Only smoking history and smoking intensity were significant. No lung cancers were observed in non-smokers, and a dose response was found, with the risk of lung cancer increasing with the number of packs smoked per year.

However, among HIV-negative women, lung cancers only occurred in women who smoked at least 20 packs per year, whereas in the women with HIV, most of the cancers (seven) were seen in those who smoked between ten and twenty packs per year (incidence, 246 per 100,000 person years). The investigators speculate that “HIV may have accelerated the development of lung cancer.”

Women who developed cancer smoked a median of 19 packs of cigarettes per year, which was significantly higher than the median nine packs per year consumed by smokers who did not develop cancer (p = 0.002).

Finally, the investigators examined the characteristics of the HIV-positive women who developed lung cancer.

Their median age was 53 years, and all were non-Hispanic black. Median annual cigarette consumption was 15 packs.

At the time of lung cancer diagnosis, only two of the women were taking potent, triple-drug antiretroviral therapy. Median CD4 cell count was 376 cells/mm³ and median viral load was 3400 copies/ml. Two-thirds of the women had a history of AIDS-defining illnesses.

Median survival after the diagnosis of lung cancer was 14 months, and one woman was still alive after 28 months.

“When compared to population-based controls, any increase in the incidence of lung cancer among HIV-infected women could be explained by differences in the history of tobacco exposure”, comment the investigators.

They conclude, “the development of lung cancer among HIV-infected women appears very strongly correlated with tobacco exposure. As such, the development and implementation of smoking cessation programmes aimed at HIV-infected persons will be of increasing importance. The precise role of HIV infection, per se, in the development of progression of lung cancer awaits further clarification.”