An old video [1] in response to this old article may indicate another reason why elephants dont get cancer, and provide easier way to replicate those results than gene therapy or splicing. Hint: go vegan.
There are studies on this, however they are controversial since diet is not easy to control amongst study subjects. Also, there are vested interests keeping public opinion divided on this matter.
> Conclusion: Vegetarian diets seem to confer protection against cancer.
> Impact: Vegan diet seems to confer lower risk for overall and female-specific cancer compared to other dietary patterns. The lacto-ovo-vegetarian diets seem to confer protection from cancers of the gastrointestinal tract.
> Abstract: The role that nutrition plays in cancer development and treatment has received considerable attention in recent decades, but it still engenders considerable controversy. Within the cancer research and especially the clinical community, for example, nutritional factors are considered to play, at best, a secondary role. The role of nutrition in cancer development was noted by authorities as far back as the early 1800s, generally under the theory that cancer is "constitutional" in its origin, implying a complex, multifactorial, multistage etiology. Opponents of this idea insisted, rather vigorously, that cancer is a local unifactorial disease, best treated through surgery, with little attention paid to the etiology and possible prevention of cancer. This "local" theory, developed during the late 1700s and early 1800s, gradually included, in the late 1800s and early 1900s, chemotherapy and radiotherapy as treatment modalities, which now remain, along with surgery, as the basis of present-day cancer treatment. This highly reductionist paradigm left in its wake unfortunate consequences for the present day, which is the subject of this perspective.
(I am citing the second publication only in defense of my original comment, for future reference. In retrospect, when discussing health benefits of diet, I should have used the term whole food plant based diet instead of vegan to avoid the baggage that term carries.)
[1] https://nutritionfacts.org/video/how-not-to-die-from-cancer/...