September 10, 2012

expert reaction to marijuana use and testicular cancer

A study published in CANCER found a link between recreational marijuana use and an increased risk of developing subtypes of testicular cancer that tend to carry a somewhat worse prognosis. A before the headlines analysis was also sent out.

Dr Paul Pharoah, Reader in Cancer Epidemiology at the University of Cambridge, said:

“This paper reposts a straightforward case-control study in which recreational drug use reported by men who had been diagnosed with germ cell cancers/tumours of the testis (TGCT) was compared with reported recreational drug use alongside a set of carefully matched controls.

“They report an association between marijuana use and an increased risk of TGCT. This association was restricted to specific subtypes of TGCT – the non-seminomas and so-called mixed tumours. This finding is not novel. A similar association, including the subtype specific effect, has previously been reported.

“Case-control studies are prone to bias, a major problem being that subjects can be more likely than others to remember/report previous behaviours accurately (‘recall bias’). Another problem is that marijuana use may simply be a correlate of another lifestyle factor that may be important in disease causation. However, this study was carefully carried out and the authors controlled for other likely causal factors. The fact that cocaine use was associated with a reduced risk of TGCT in this study suggests that recall bias is not a major problem here.

“A two-fold increase in risk associated with ‘ever use’ of marijuana appears to be a moderately strong risk factor. However, in absolute terms, the increase in risk is small. The incidence of testicular cancer is highest in all men in their late twenties at 18 cases per 100,000 men per year. Assuming that the prevalence of ever having used marijuana is 30% (data from European Monitoring Centre for Drugs and Drug Addiction) this means that marijuana use is associated with an absolute increase in risk of just 12 per 100,000 per year (0.012%) in this age group.

“The findings are biologically plausible but there is no proven mechanism to link the pharmacology of marijuana to development of testicular cancer.

“The reduced risk of TGCT associated with cocaine use is a novel finding. Again, this is biologically plausible and the effect would be considered moderately strong in relative terms with a risk of about one half, but still small in absolute terms.”

‘Population-Based Case-Control Study of Recreational Drug Use and Testis Cancer Risk Confirms an Association Between Marijuana Use and Nonseminoma Risk’ by John Charles A. Lacson et al., published in Cancer on Monday 10 September.