The risk of cancer among persons with a history of injecting drug use in Sweden - a cohort study based on participants in a needle exchange program.

Abstract Background. Injecting drug use (IDU) may lead to exposure to a range of carcinogenic agents. We investigated the risk and distribution of cancers among individuals with a history of IDU in Sweden. Material and Methods. The cancer incidence in a cohort of longitudinally followed participants in a needle exchange program (NEP), recruited between 1987 and 2007, was compared to that in the Swedish general population, matching for age group and gender. Baseline demographic and drug use data were collected and longitudinal testing of serological markers for HIV, hepatitis B and C virus was performed during NEP participation. Standardized incidence ratios (SIR) for types of cancer found in the study cohort were calculated, using data from the Swedish National Cancer Registry for reference. Results. The mean follow-up time for the 3255 participants was 11.8 years, constituting 38 419 person years at risk. The mean age at end of follow-up was 42.7 years, and 75% of participants were men. Seventy-eight cases of cancer were observed (SIR 1.1 [95% CI = 0.9-1.4]). The SIR was significantly increased for five cancer types among men; primary liver, laryngeal, lung, oropharyngeal and non-melanoma skin cancer (respective SIR 12.8 [95% CI = 4.2-30.0], 9.2 [95% CI = 1.9-26.8], 3.2 [95% CI = 1.5-6.1], 7.3 [95% CI = 1.5-21.2], and 3.5 [95% CI = 1.1-8.2]), and for cancers of endocrine organs among women (5.3 [95% CI = 1.7-12.4]). Conclusion. Although the standardized overall cancer incidence in this relatively young IDU cohort was similar to that in the general population, the risk of specific types of cancer was significantly increased, suggesting that IDU confers elevated risks for certain malignancies. These findings prompt further studies to investigate causative factors and suggest the need for surveillance among persons with a history of IDU.