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