So there are conflicting studies present concerning the subject at hand, and this is mostly due to a multi-causal situation, when we have several factors present that interchange each other. This is the presence of an anti-cancerogenetic vector in the form of various cannabinoids, but foremostly THC:
"THC and CBD can induce signs of apoptotic and necrotic cell death in tumor cells."
https://de.wikipedia.org/wiki/Tetrahydrocannabinol#Pharmakologie"
The problem of conflicting results from studies is well known through the scientific world and has several reasons. Actually there are systematics present to mitigate this and still combine the results in a true manner ("Meta-Studies") and here the empirical data gathered from the US health sectors show this relationship:
- lowest risk of lung cancer: (0% of rel.) 0% smoke nor substance
- INsignificant increase in lung cancer (~1% of rel.): strict MJ only smoker
- very high & highest risk in lung cancer: (100% of rel.) tobacco smoker
- INsignificant decrease in lung cancer: (98% of rel.) tobacco & MJ smoker
The explanation is that cannabis contains suppressors of cancercells and its presence enables natural killercells and cytotoxical T-cells to induce Apoptosis (a self-destruct program which enables our immunesystem to order a controlled self-deconstruct mechanism after the cell has been found to produce foreign antigenes, typically displayed at the MHC-I receptor epitope. It is one of the seven stages of onkogenese which causes this self-control mechanism to not work properly anymore, but the presence of THC or other cannabinoids have shown to hinder the evil mutation to do its job.
But there are many forms of cancers and also the plant material contains different carcinogenetic agents, so the main conclusion that can be drawn from this relationship is that, in most cases, tobacco is responsible for lung cancer - and not cannabis.
The question is actually whether the amount of reduction of cancercases in combined smokers far outweigh the increase in a tiny amount of strict users. Or if it's actually worth to talk about the insignificant cases (and draw conclusions from it) when the 100% & 98% numbers clearly reveil the culprit!