Processed, polyunsaturated seed oils are rich in linoleic acid, which promotes cancer in rodents.

http://www.ncbi.nlm.nih.gov/pubmed/3921234

Requirement of essential fatty acid for mammary tumorigenesis in the rat.
http://cancerres.aacrjournals.org/content/4/3/153.full.pdf

However, when the corn oil was replaced by hydrogenated coconut oil the tumor incidence never exceeded 8 percent, while in most groups it was zero.
https://pdfs.semanticscholar.org/b44f/0f82cbb7d9473ac99c3866...

Thus the substitution of hydrogenated coconut oil for corn oil definitely inhibited tumor induction...
https://www.ncbi.nlm.nih.gov/pubmed/6704963

These findings suggest that dietary unsaturated fats have potent cocarcinogenic effects on colon carcinogenesis.
http://www.ncbi.nlm.nih.gov/pubmed/6815624

Inhibitory effect of a fat-free diet on mammary carcinogenesis in rats.
https://link.springer.com/article/10.1007/BF02531379

Experiments with 10 different fats and oils fed at the 20% level indicated that unsaturated fats enhance the yield of adenocarcinomas more than saturated fats.
https://www.ncbi.nlm.nih.gov/pubmed/7285004

Thus, diets high in unsaturated fat appear to promote pancreatic carcinogenesis in the azaserine-treated rat while a diet high in saturated fat failed to show a similar degree of enhancement of pancreatic carcinogenesis.
https://www.ncbi.nlm.nih.gov/pubmed/6577233

...tumors grew to a larger size in C3H mice fed the 10% corn oil diet...than in those fed the 10% hydrogenated oil diet (without linoleate). The C3H mice fed diets with 1% linoleic acid developed significantly larger tumors than did those fed 1% oleic acid...
https://www.ncbi.nlm.nih.gov/pubmed/6587159

...corn oil (CO) diet, which contains linoleate...hydrogenated cottonseed oil (HCTO), a diet free of the polyunsaturated fatty acid...Both incidence and growth rate of tumors...were greater in mice fed diets containing either 0.3, 1, or 10% CO than in those fed 10% HCTO.
https://www.ncbi.nlm.nih.gov/pubmed/1255775

...mammary tumor growth was depressed by a fat-free or saturated-fat diet and enhanced by dietary linoleate.
https://www.ncbi.nlm.nih.gov/pubmed/817101

The cumulative incidence of tumor-bearing rats among DMBA-dosed rats was greater when the polyunsaturated fat diet was fed
https://www.ncbi.nlm.nih.gov/pubmed/3459924

...animals fed the HF safflower and corn oil diets exhibited enhanced mammary tumor yields when compared to animals fed HF olive or coconut oil diets...
https://www.ncbi.nlm.nih.gov/pubmed/107358

These results show that a certain amount of polyunsaturated fat, as well as a high level of dietary fat, is required to promote mammary carcinogenesis.
https://www.ncbi.nlm.nih.gov/pubmed/6782319

...the addition of 3% ethyl linoleate (an ethyl ester of a polyunsaturated fatty acid) increased the tumor yield to about twice that in rats fed either the high-saturated fat diet or a low-fat diet.
https://www.ncbi.nlm.nih.gov/pubmed/3476922

...animals fed HF diets rich in linoleic acid, such as safflower and corn oil, exhibited increased incidence and decreased latent period compared with...animals fed HF diets rich in oleic acid (olive oil) or medium-chain saturated fatty acids (coconut oil).
https://www.ncbi.nlm.nih.gov/pubmed/416226

The differences in tumor incidence suggest that carcinogenesis was enhanced by the polyunsaturated fat diet during the promotion stage of carcinogenesis.
https://www.ncbi.nlm.nih.gov/pubmed/6488161

...they suggest an association between promotion of mammary cancer and elevated levels of linoleic acid in serum lipids.
https://www.ncbi.nlm.nih.gov/pubmed/2979798

These results suggest that a diet high in unsaturated fat alone, or in combination with 4% cholestyramine, promotes DMBA-induced mammary cancer in Wistar rats.
https://www.ncbi.nlm.nih.gov/pubmed/26091908

Groups of animals fed the corn oil-enriched diet showed the highest percentage of tumor-bearing animals, significantly different in comparison with control and HOO groups. Total number of tumors was increased...
https://www.ncbi.nlm.nih.gov/pubmed/6583457

...effect of dietary corn oil (CO), safflower oil (SO), olive oil (OO), coconut oil (CC), and medium-chain triglycerides (MCT)...The incidence of colon tumors was increased in rats fed diets containing high-CO and high-SO...whereas the diets containing high OO, CC, or MCT had no promoting effect on colon tumor incidence.
https://www.ncbi.nlm.nih.gov/pubmed/6778606

...an increase in fat intake was accompanied by an increased tumor incidence when corn oil was used in the diets. A high saturated fat ration, on the other hand, was much less effective in this respect.
https://www.ncbi.nlm.nih.gov/pubmed/9066676

The promotive tumorigenic effects of the other high-fat diets were associated with their high levels of some polyunsaturated fatty acids...
https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1751-1097....

Mice fed 20% saturated fat were almost completely protected from UV tumorigenesis when compared with mice fed 20% polyunsaturated fat.
https://www.ncbi.nlm.nih.gov/pubmed/8973605

...the highest tumour [loads] (fed 15% or 20% polyunsaturated fat),... in comparison with the mice bearing smaller tumour loads (fed 0, 5% or 10% polyunsaturated fat).
https://www.ncbi.nlm.nih.gov/pubmed/27033117

...we found an inverse association between SF content and tumor burden...at least in male mice; there was a decrease in mortality in mice consuming the highest concentration of SFAs.
https://www.ncbi.nlm.nih.gov/pubmed/7214328

Increased tumor incidence and decreased time to tumor were observed when increasing levels of linoleate (18:2)...Increasing levels of stearate were associated with decreased tumor incidence and increased time to tumor.
https://www.ncbi.nlm.nih.gov/pubmed/1732055

A positive correlation between level of dietary LA and mammary tumor incidence was observed
https://www.ncbi.nlm.nih.gov/pubmed/6064952

Enhancement of mammary carcinogenesis in the high-corn oil diet group is detectable in most of the parameters studied.
https://pubmed.ncbi.nlm.nih.gov/8317898/

...increased the tumor number of rats fed corn oil, but not those fed palm oil....