Kucuk pointed out that while this was the first paper amid limited research on marijuana and cancer to show a causal effect, there is evidence that marijuana does affect parts of both the male and female reproductive systems, including hormones and sperm quality.
In addition, Stephen Schwartz, co-author of the study, epidemiologist and member of the Public Health Sciences Division at the FHCRC, indicated that there may be room for improving the quality of the data gathered.
"We're reliant on them telling us what they did," Schwartz said. "We have to be a little skeptical of the accuracy of the reporting."
But the results showing that men with the aggressive, nonseminomal testicular cancer were more frequent drug users than those with seminomal cancer made Daling believe that patients were telling the truth overall, or were at least being consistent in their answers.
"If, when you're doing a cancer study, you might suspect that the cancer cases might be more honest when answering a question that is not routine," Daling said. "If that was the case, you'd see it across both histology groups. But we saw it only in nonseminomas, which indicates it's not just recall bias."
More substantial research on marijuana use being linked to increased risk for lung, head and neck cancers does exist, although it is not definitive. Kucuk said that trying to uncover the mechanism of how marijuana might be associated with cancer -- whether it could be hormonal or receptor-related -- could help focus future studies.
"Research like this is not meant for people to change their habits or ideas," Schwartz said. "It is one study out of many more that need to be done."
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