A 2016 review of cannabinoid therapies in oncology included 11 preclinical studies of their use in the treatment of malignancies.3 One of the first, in 1975, found that some cannabis extracts inhibited the growth of lung adenocarcinoma cells in vitro.4 Others, the review noted, examined the effects of cannabinoids on lung, glioma, thyroid, lymphoma, skin, pancreas, endometrium, breast, and prostate cancers, “demonstrating antiproliferative, anti-metastatic, antiangiogenic, and proapoptotic effects.”

The NCI similarly identified more than 30 preclinical studies of the antitumor effects of a variety of cannabinoids, ranging from a study in mice and rats showing a potential protective effect that resulted in a decreased incidence of particular cancers to an in vitro study of breast cancer cell lines, which found that CBD induced programmed cell death.

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All of those, though, involved either in vitro or in vivo studies, not human trials. And, as Donald Abrams, MD, chief of the hematology-oncology division at San Francisco General Hospital in California, wrote in a 2016 paper:

“Mice and rats are not people, and what is observed in vitro does not necessarily translate into clinical medicine. The preclinical evidence that cannabinoids might have direct anticancer activity is provocative as well, but more research is warranted.”5

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Human trials focus primarily on the palliative effects of cannabinoids. In fact, as a number of articles over the years have remarked, there is only one clinical study published to date.6

That one, a pilot phase 1 trial, involved an exceedingly small sample — 9 patients with recurrent glioblastoma multiforme. The trial was, Dr Velasco said, designed to determine the safety and toxicity of intracranial administration of Δ9-Tetrahydrocannabinol (THC). The study demonstrated antiproliferative effects, however, in 2 of the patients.

“It was promising to see that there were 2 patients who lived longer than expected,” he said, “but you couldn’t extract any statistical conclusions from this type of study.”