Methadone maintenance and cancer risk: an Israeli case registry study.

OBJECTIVES

This study explored cancer incidence rates in a large cohort of Israeli (Jewish and Arab) opioid-dependent individuals receiving methadone maintenance treatment (MMT), and how the incidences vary by ethnicity and sex.

METHOD

The record linkage between the Israel National Addiction Registry (INAR) and the Israel National Cancer Registry (INCR) was performed. Information about the Israeli general population from the Central Bureau of Statistics was used for comparison to match sex and year of birth to the cohort under study. Age standardized incidence ratios (SIRs) and 95% confidence intervals (CIs) were calculated.

RESULTS

Though the SIR values for aggregated cancer sites for both men and women on MMT did not differ significantly from the corresponding figures in the general population (0.88, 95% CI 0.76-1.00, and 1.06, 95% CI 0.76-1.36, respectively), the risks were substantially increased for lung (1.97, 95% CI 1.13-2.82), larynx (3.62, 95% CI 1.11-6.13) and liver (6.8, 95% CI 1.76-11.83) cancers among Jewish men and for cervix uteri cancer among Jewish women (2.41, 95% CI 0.99-3.84). By contrast, the SIR values for colorectal cancer among Jewish men (0.46, 95% CI 0.09-0.82) and for breast cancer among Jewish women (0.36, 95% CI 0.00-0.71) were significantly lower than expected.

CONCLUSIONS

The results suggest that the increased and reduced site-specific cancer risks are counterbalanced, resulting in the absence of the expected excess cancer risk for the entire cohort. The reduced risks for colorectal and breast cancers suggest a protective effect of MMT, warranting further investigation.