A comprehensive list of studies that describe the treatment of various cancers with cannabinoids. Unlike tobacco, dagga has some chemicals that inhibit many types of cancer cells, effectively cancelling out any carcinogens, and in some cases promoting tumor reduction / elimination.
Lung
http://www.ncbi.nlm.nih.gov/pubmed/22198381
http://www.ncbi.nlm.nih.gov/pubmed/21097714
http://www.nature.com/onc/journal/v27/n3/abs/1210641a.html
Uterine, Testicular, and Pancreatic
http://www.cancer.gov/cancertopics/pdq/cam/cannabis/healthprofessional/page4
http://cancerres.aacrjournals.org/content/66/13/6748.abstract
Prostate Cancer
http://www.ncbi.nlm.nih.gov/pubmed/12746841?dopt=Abstract
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3339795/?tool=pubmed
http://www.ncbi.nlm.nih.gov/pubmed/22594963
Colorectal
http://www.ncbi.nlm.nih.gov/pubmed/22231745
https://www.ncbi.nlm.nih.gov/pubmed/19442536
http://safeaccess.ca/research/pdf/MD_AndersonCancerStudy.pdf
http://gut.bmj.com/content/54/12/1741.abstract
http://www.ncbi.nlm.nih.gov/m/pubmed/25269802/
Ovarian
http://www.aacrmeetingabstracts.org/cgi/content/abstract/2006/1/1084
Blood
http://www.ncbi.nlm.nih.gov/pubmed/12091357
http://www.ncbi.nlm.nih.gov/pubmed/16908594
http://onlinelibrary.wiley.com/doi/10.1002/ijc.23584/abstract
http://molpharm.aspetjournals.org/content/70/5/1612.abstract
http://www.ncbi.nlm.nih.gov/m/pubmed/18546271/
Skin
http://www.ncbi.nlm.nih.gov/pubmed/12511587
Liver
http://www.ncbi.nlm.nih.gov/pubmed/21475304
Biliary Tract
http://www.ncbi.nlm.nih.gov/pubmed/19916793
Brain
http://www.nature.com/bjc/journal/v95/n2/abs/6603236a.html
http://www.ncbi.nlm.nih.gov/pubmed/11479216
http://www.jneurosci.org/content/21/17/6475.abstract
http://jpet.aspetjournals.org/content/308/3/838.abstract
http://mct.aacrjournals.org/content/10/1/90.abstract
http://www.ncbi.nlm.nih.gov/pubmed/17952650
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1576089/
http://www.jci.org/articles/view/37948
http://cancerres.aacrjournals.org/content/64/16/5617.full
Mouth and Throat
http://www.ncbi.nlm.nih.gov/pubmed/20516734
Breast
http://www.ncbi.nlm.nih.gov/pubmed/20859676
http://www.ncbi.nlm.nih.gov/pubmed/18025276
http://www.ncbi.nlm.nih.gov/pubmed/21915267
http://jpet.aspetjournals.org/content/early/2006/05/25/jpet.106.105247.full.pdf+html
http://www.molecular-cancer.com/content/9/1/196
http://www.ncbi.nlm.nih.gov/pubmed/22776349
http://www.pnas.org/content/95/14/8375.full.pdf+html
http://cancerres.aacrjournals.org/content/66/13/6615.abstract
http://endo.endojournals.org/content/141/1/118.abstract#fn-1
Others
http://www.ncbi.nlm.nih.gov/pubmed/12514108
http://www.ncbi.nlm.nih.gov/pubmed/15313899
Source
The list compiled by patchgrabber on reddit.com