You’d think it would have been very big news in the spring of 2005 when Donald Tashkin, a professor of pulmonology at UCLA’s David Geffin School of Medicine, revealed at a conference that components of marijuana smoke, although they damage cells in respiratory tissue, somehow prevent them from becoming malignant. But headlines announcing “Pot Doesn’t Cause Cancer” did not ensue.
Tashkin will review his findings and discuss current research this Thursday in Santa Monica, California as part of a course for doctors accredited by the University of California San Francisco. (It is open to the public; pre-registration is $95.)
Tashkin has special credibility. He was the lead investigator on studies dating back to the 1970s that identified the compounds in marijuana smoke that are toxic. It was Tashkin who published photomicrographs showing that marijuana smoke damages cells lining the upper airways. It was the Tashkin lab reporting that benzpyrene — a component of tobacco smoke that plays a role in most lung cancers — is especially prevalent in marijuana smoke. It was Tashkin’s data documenting that marijuana smokers are more likely than non-smokers to cough, wheeze and produce sputum.
The National Institute on Drug Abuse supported Tashkin’s marijuana-related research over the decades and gave him a grant to conduct a large, population-based, case-controlled study that would prove definitively that heavy, long-term marijuana use increases the risk of lung and upper-airways cancers. What Tashkin and his colleagues found, however, disproved their hypothesis.
Tashkin’s team interviewed 1,212 cancer patients from the Los Angeles County Cancer Surveillance program, matched for age, gender, and neighborhood with 1,040 cancer-free controls. Marijuana use was measured in “joint years” (number of years smoked times number of joints per day). It turned out that increased marijuana use did not result in higher rates of lung and pharyngeal cancer (whereas tobacco smokers were at greater risk the more they smoked). Tobacco smokers who also smoked marijuana were at slightly lower risk of getting lung cancer than tobacco-only smokers.
The Tashkin scoop was still there for the taking in April 2009 when Tashkin reviewed his findings at a conference at Asilomar organized by “Patients Out of Time.” Investigators from New Zealand had recently gotten widespread media attention for a study contradicting Tashkin’s results. “Heavy cannabis users may be at greater risk of chronic lung disease –including cancer– compared to tobacco smokers,” is how BBC News summed up the New Zealanders’ findings. The very small size of the study –79 smokers took part, 21 of whom smoked cannabis only– was not held against the authors. As conveyed in the corporate media, the New Zealand study represented the latest word on this important subject.
Tashkin criticized the New Zealanders’ methodology in his talk at Asilomar: “There’s some cognitive dissonance associated with the interpretation of their findings. I think this has to do with the belief model among the investigators and –I wish they were here to defend themselves — the integrity of the investigators… They actually published another paper in which they mimicked the design that we used for looking at lung function.”