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I see this popping up on my Facebook feed quite a lot (to be fair, it's usually the same 3 people): Claims that evidence has shown that marijuana/cannabis/THC can have a positive effect in cancer treatment. I wonder what the truth is behind this, as based on the reporting, I'm sure it's being exaggerated by heavily-biased parties.

Examples:

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I'm not sure this is the right claim to be entirely honest. Most of the support for THC in cancer treatment is for it's ability to mitigate the negative/painful side effects of chemotherapy, etc.; not for it's ability to actually directly treat cancer. –  LessPop_MoreFizz Dec 19 '12 at 2:19
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Yes, most of it is, and I think that's nearly generally accepted at this point. But I have also seen a lot of claims that THC will slow/cure more than just the symptoms, and that's what I wanted to get more info about. –  Damon Dec 19 '12 at 17:29
    
I suggest that everyone watch "Rick Simpson - Run from the Cure" on Youtube, if you're still skeptical after watching, then stick with Chemo. –  user11030 Jan 10 '13 at 4:33
    
It's true that pro-weed parties are "heavily biased" however not nearly as much as the "reefer madness" bias that put them in this position in the first place. Interestingly, MDMA (ecstasy) has been proven to treat cancer. telegraph.co.uk/science/science-news/8709920/… –  rickyduck Jan 10 '13 at 9:07

2 Answers 2

The answer is yes, in laboratory experiments, and perhaps in a clinical setting as well.

Let me emphasize: the proof exists in controlled laboratory experiments. It has not been demonstrated to be true in human trials. So don't smoke up in the expectation that it's a better cancer treatment than a doctor's recommendations (generally chemotherapy, radiation therapy, or surgery, but would vary from patient to patient).

An article by Guzman in 2003 states that:

In addition, these compounds have been shown to inhibit the growth of tumour cells in culture and animal models by modulating key cell-signalling pathways. Cannabinoids are usually well tolerated, and do not produce the generalized toxic effects of conventional chemotherapies.

The question, at the time, is what the causal relationship is to inhibiting tumor growth. The answer to that question is apparently dependent on the type of cancer.

For instance, in prostate cancer, a metastudy (Ramos and Bianco, 2012) found that:

Prostate cancer cells possess increased expression of both cannabinoid 1 and 2 receptors, and stimulation of these results in decrease in cell viability, increased apoptosis, and decreased androgen receptor expression and prostate-specific antigen excretion.

In other words, cannabis causes increased prostate cancer cell death. They suggest that more study is warranted:

It would be of interest to conduct clinical studies utilizing cannabinoids for patients with metastatic prostate cancer, taking advantage not only of its beneficial effects on prostate cancer but also of their analgesic properties for bone metastatic cancer pain.

A similar story (Greenhough et al, 2007) appears to hold true in colorectal cancer:

... the mechanisms underlying the antitumoral effects of cannabinoids are incompletely understood, and evidence suggests these effects may be cell-type specific. Two signalling pathways that have been reported to be either positively or negatively regulated by cannabinoids (depending on the cell type and cannabinoid studied) are the RAS-MAPK/ERK pathway and the PI3K-AKT pathway. ... Here, we show, for the first time, that THC induces apoptosis in colorectal cancer cells, and that this occurs through the activation of the CB1 cannabinoid receptor. THC treatment resulted in the inhibition of both RAS-MAPK and PI3K-AKT survival signalling cascades

These two articles provide very specific pathways for cannabinoids to inhibit tumor growth and reduce existing tumor extent, but it's important to note that both are based on work in the lab. The call for bringing the prostate cancer work into more general therapeutic practice demonstrates that this is not, yet, a proven cancer therapy.

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Meh... that was done on cell cultures, by putting the drug directly in the culture medium, which is a fairly poor model when looking at something as complex as cancer (you know, cell cultures do not have blood circulations, a liver, fat, a brain etc. for instance). Some animal studies are necessary before anything can be said, but it does not seem they have really been done yet. A different story, obviously, is the use of THC in cancer pain management. –  nico Jul 24 '12 at 6:34
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@nico-- agreed. I thought I had that caveat pretty well explained in the answer; did I not make it clear? –  mmr Jul 24 '12 at 13:42
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I think it is quite clearly explained in the references, however I was just pointing out those things because I think someone who is not used to reading biology papers may not quite get those "subtilities". –  nico Jul 24 '12 at 14:28
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I didn't check the references in detail, but if it's only cell-culture results, I'd personally add some stronger disclaimers on the results. In my observation, non-scientist tend to vastly overestimate such results, we need to put such data in context and make clear how far this is from something like a double-blind clinical study. –  Fabian Jul 24 '12 at 19:29
    
@Fabian: I only checked them quickly and did not go through all of the refs, so I may have missed something. –  nico Jul 25 '12 at 16:45

The answer is DEFINITELY yes, THC can cure or slow cancer. It has already been tested in vitro AND in vivo; in mice and rats AND in nine people with advanced brain tumour with varying but positive results.

It seems to stop cancer cells growth, avoid their "feeding" mechanism, reduce their proliferation AND, imho, its most promising characteristic, do all this "respecting" healthy cells nearby.

BUT, and there are some "buts": But, ;-) instead of copying I'll link the article from Dr Manuel Guzman that kind of seems to have heard your question:

http://www.cannabis-med.org/index.php?tpl=faq&red=faqlist&id=274&lng=en

He says it all.

@Fabian & @nico Dr Guzman agrees with you.

These are other references that back my words:

http://www.cancer.gov/cancertopics/pdq/cam/cannabis/healthprofessional/page4

http://www.molecular-cancer.com/content/9/1/196

http://www.jci.org/articles/view/37948

http://en.wikipedia.org/wiki/Medical_cannabis

Sativex has already been tested throughout Europe with positive results.

http://www.cannabis-med.org/english/bulletin/ww_en_db_cannabis_artikel.php?id=393#2

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So, in his third sentence he says "However, at the moment there is not solid evidence to prove that cannabinoids –whether natural or synthetic- can effectively treat cancer in patients, although research is ongoing around the world." Doesn't that contradict your first sentence? –  Oddthinking Feb 27 '13 at 0:10

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