After applying exclusion criteria, 45 412 individuals registered for OST between 1985 and 2007 were included in the study cohort (). This cohort accumulated 481 936 person-years of follow-up for cancer, a median of 9.9 person-years per registrant (IQR 5.61–15.2; ). Two-thirds of the cohort was male. The median age at OST registration was 27 years and the median cumulative time on OST was 2.6 years (IQR 0.6–6.5). A total of 423 (0.8%) registrants were notified with an HIV/AIDS diagnosis prior to or after OST registration.
Characteristics of all New South Wales opioid substitution therapy registrants and those with notified HIV infection, 1985–2007
We observed 819 (1.8%) incident primary cancers (803 first, 16 second cancers) after OST registration and the median age at diagnosis of first cancer was 43 (IQR 37–49) years.
After applying further exclusion criteria, the subcohort with assessable hepatitis data comprised 29 613 participants entering OST between 1993 and 2007 (). They were of similar age and sex as the full cohort (median age at OST registration, 26 years; 69% male). A total of 14 892 (50%) registrants were notified with HCV alone, 598 (2%) with HBV alone, and 898 (3%) with HBV and HCV. Over the 213 008 person-years of follow-up in the subcohort, 240 (0.8%) incident cancers were observed.
Characteristics of New South Wales opioid substitution therapy registrants, by BBV notification status, 1993–2007
For the period 1985–2007 the crude cancer incidence rate was 170/100 000 person-years (95% CI 159 to 182). The age-standardised rate was 349/100 000 person-years (95% CI 337 to 361) and the annual age-standardised rate increased significantly between 1985 and 2007 (AAPC=9.4%, 95% CI 4.2% to 15%; p=0.001).
Risk of cancer overall was slightly higher in OST registrants compared to the Australian population (SIR=1.15, 95% CI 1.07 to 1.23). SIRs were significantly greater than unity for cancers of the tonsil, anus and anal canal, liver, pancreas, larynx, trachea bronchus and lung, vulva and cervix, Kaposi sarcoma, non-Hodgkin's lymphoma and cancer of unknown primary site (). Conversely, SIRs were significantly less than unity for melanoma and cancers of the colorectum, breast, prostate, brain and central nervous system and thyroid.
Figure 1 Risk of cancer among New South Wales opioid substitution therapy registrants, 1985–2007. CNS, central nervous system; Exp, expected number of cancers; Obs, observed number of cancers; SIR, standardised incidence ratio. *Includes non-Hodgkin's (more ...)
Risk of any cancer was significantly increased in men and in those more than 40 years of age (). Liver and lung cancer risk was increased in men and women; liver cancer risk was significantly increased only for those more than 40 years of age, while lung cancer risk was increased regardless of attained age. Similarly, women of all ages experienced half the risk of breast cancer.
Risk of any cancer and the most frequently occurring cancers in New South Wales opioid substitution therapy registrants, by sex and current age (1985–2007)
BBVs and cancer risk
Thirty-four cancers were observed in registrants notified with HIV (irrespective of infection with other BBVs), with an SIR of 6.68 (95% CI 4.63 to 9.34; ). SIRs were significantly greater than unity for several cancers, including Kaposi sarcoma, non-Hodgkin's lymphoma and anal cancer.
Figure 2 Risk of cancer in New South Wales opioid substitution therapy registrants with notified HIV infection, 1985–2007. Exp, expected number of cancers; Obs, observed number of cancers; SIR, standardised incidence ratio. *Includes (more ...)
In those notified with HCV monoinfection, the overall risk of cancer was not significantly different from that of the general population (SIR=1.06, 95% CI 0.89 to 1.25; ) but the SIR for liver cancer was 6.61 (95% CI 3.02 to 12.5). After adjusting for an assumed age of HCV infection of 25 years and for survival, the SIR for liver cancer increased to 13.1 (95% CI 6.00 to 24.9). Risk of lung cancer and mouth cancer were also elevated. On the contrary, breast cancer risk was decreased and while six prostate cancers were expected, none were observed. Few cancers were observed in those notified with HBV (one case) or HBV-HCV co-infection (18 cases). The risk of liver cancer in individuals notified with HBV-HCV co-infection was markedly elevated (SIR=35.9, 95% CI 7.41 to 105).
Figure 3 Risk of cancer among New South Wales opioid substitution therapy registrants with notified hepatitis C infection and registrants without notified hepatitis B, hepatitis C or HIV infection, 1993–2007. *Includes non-Hodgkin lymphoma not otherwise (more ...)
Registrants without a notification of BBV infection were at decreased risk of cancer overall (SIR=0.68, 95% CI 0.54 to 0.84; ) and melanoma. In this subgroup, no infection-related cancers occurred at rates significantly different to the general population; however, the risk of pancreatic cancer was significantly elevated.
In multivariable analyses adjusting for age, calendar year, sex and HCV, HBV and HIV notification status, age was an independent risk factor for the most frequently occurring cancers (). Notification of HBV and HCV infection predicted risk of liver cancer, and notification of HIV infection predicted risk of non-Hodgkin's lymphoma. Notification of HCV infection independently predicted risk of lung cancer.
Multivariable analysis of risk factors for common cancers among New South Wales opioid substitution therapy registrants, 1993–2007