According to a recently published national study, HIV-related immunosuppression is linked with lung cancer risk. Factors that measure function of the immune system, such as CD4 cell count and CD4/CD8 ratio, were associated with increased risk of lung cancer. Also associated with lung cancer risk was history of bacterial pneumonia episodes.
Human immunodeficiency virus, otherwise known as HIV, is the virus that causes progressive failure of the immune system and can result in acquired immunodeficiency syndrome (AIDS) overtime. HIV infects vital cells of the immune system, particularly those that carry the identity of being CD4 positive, such as T cells and macrophages. When left untreated, the virus can kill these immune cells that assist in the fight against infection and cancer. As a result, the individual is at increased susceptibility to disease. The most common cancer in individuals with HIV is lung cancer, even after accounting for risk factors like age, smoking and other lung diseases. It remains unclear, however, if the degree of immune deficiency in HIV+ patients is related to the risk of developing lung cancer. Previous studies investigating this relationship have been limited by low cohort numbers and poor measures of immunosuppression.
In their study, Sigel and the study team at the School of Medicine at Mount Sinai sought to evaluate the association between degree of immunosuppression and risk of developing lung cancer. The authors followed a large group of 21 666 patients with HIV from the Veterans Aging Cohort Study from January 1st, 1998 through to December 31, 2012, and established laboratory immune markers of CD4 cell count, CD8 cell count, and CD4/CD8. This data was linked with the Veterans Affairs Central Cancer Registry, containing information on confirmed cases of lung cancer among patients with HIV in the cohort. They adjusted for proven confounding factors, including age, ethnicity, smoking, alcohol use and clinical diagnoses of other lung diseases, such as chronic obstructive pulmonary disease. They then used statistical tests to compare immune characteristics of those patients who developed lung cancer and those that did not.
The study, published in The Lancet HIV, found that HIV-related immunosuppression is linked with lung cancer risk. More specifically, HIV-positive patients with a continuously low CD4 cell count were at increased risk of developing lung cancer compared to those with a higher CD4 cell count. The ratio of CD4/CD8 was also continuously lower in patients who eventually developed lung cancer compared to those that did not. Interestingly, more cumulative episodes of bacterial pneumonia in this patient population were also associated with increased risk of lung cancer. These characteristics are all indicative of extensive immunosuppression. There are limitations of this study, however; mainly that the cohort was comprised predominantly of men and the results of this study may therefore not be transferred to all individuals living with HIV.
The findings of this study suggest that HIV-related immunosuppression is a strong predictor of lung cancer risk. This opens up the possibility that laboratory and clinical measures of immune function, such as CD4/CD8 ratio and history of bacterial pneumonia, could be used to target high-risk HIV-positive individuals with lung cancer preventative measures.
Written By: Danielle Vitali, BSc