Like tobacco smoking, marijuana smoking has been implicated as a causative factor in tumors of the head and neck and of the lung.

The marijuana smokers in whom these tumors occur are usually much younger than the tobacco smokers who are the usual victims of these malignancies. A question remains as to whether transitional cell carcinoma (TCCA), highly linked to tobacco use, can also be linked to marijuana use and if the cancers seen in marijuana smokers are similar to those seen in tobacco users.

A recent paper by J. A. Chacko and colleagues from the Medical College of Georgia and Stanford University examines the relationship between marijuana use and TCCA. The manuscript is published in the January 2006 issue of Urology.

Fifty-two men aged less than 60 years presenting consecutively with transitional cell carcinoma and 104 age-matched controls completed questionnaires about exposure to various potential carcinogens including radiation, Agent Orange, smoked or processed meats, dyes, tobacco, and marijuana. The patients all presented to one of two VA hospitals, the Augusta, Georgia VA and the Palo Alto, California VA.

Analysis of the results showed that there was no difference in the exposure histories between the two VA hospitals. Of the 52 patients with TCCA, 46 (88.5%) reported a history of habitual marijuana usage, and 72 (69.2%) of the 104 age-matched controls gave a history of habitual marijuana use. This difference was statistically significant (P = 0.008). The cancer patients also demonstrated a significantly higher quantity of marijuana use in joint-years (P = 0.022), with a mean of 48 joint-years, compared to 28.5 joint-years for the control group. Both the cancer patients and the control group had tobacco use rates in excess of 90%. In this small number of patients, no relationship could be identified between marijuana use and/or tobacco use or quantity and tumor grade, stage, and recurrence rates.

Although this study suggests and causal relationship between marijuana exposure and bladder cancer, larger-scale epidemiologic and basic science studies are needed to confirm the role of marijuana smoking as an etiologic agent in the development of transitional cell carcinoma.

By Michael J. Metro, MD