According to a recent study titled, The global burden of cancer attributable to risk factors, 2010–19: a systematic analysis for the Global Burden of Disease Study 2019, "the leading risk factors at the most detailed level globally for risk-attributable cancer deaths and DALYs in 2019 for both sexes combined were smoking, followed by alcohol use and high BMI." This study was based on humans, but it is only logical that the same be true for our animals. And in humans, cancer is the second leading cause of death worldwide.
The article also states that "although some cancer cases are not preventable, government can work on a population level to support an environment that minimizes exposure to known cancer risk factors."
Yes, that would be awesome, but trusting the government anytime soon to support an environment that minimizes exposure to cancer risks, like eating a healthy diet is not going to happen anytime soon.
You have to remember that the vet business is a business with the endgame of making a profit, keeping animals alive, but not curing them or keeping them healthy. A healthy pet is no longer a customer and that is not what they want. They want to keep you and your dog hooked and will advertise kibble as healthy or safe, which then the confusion becomes more compounded because your vet recommends it. Unfortunately, vet schools are funded by the dog food guy, the dog food guy is also owned by the vaccine guy and the vaccine guy makes the laws on what makes what legal and what is approved. The dog food guy is also friends with the vet board guy because the vet board guy is funded by the vaccine guy. And all of these guys care about profit. Not you or your dogs' wellbeing.
I think it is also a safe assumption to make that most dogs don't smoke or drink alcohol, although they could be exposed to second hand smoke, but many are absolutely fed kibble, which contributes to a high BMI and overall metabolic health dysfunction. This evidenced by the bajillion dollars a year earned by behemoth companies like MARs Inc. or Nestle Purina who have monopolized the vet industry. People are obviously feeding their dogs this stuff, perhaps because they don't know any better or because they don't have the means or resources to feed a higher quality diet, which is inherently unfair to begin with.
Despite this inequity, it is a fact that foods that are manufactured at extremely high temperatures, like kibble, are extremely high in advanced glycation end products, which are proteins or lipids that become glycated as a result of exposure to sugars. They are a bio-marker implicated in aging and the development, or worsening, of many degenerative diseases, such as cancer, diabetes, atherosclerosis, chronic kidney disease, and Alzheimer's disease
Bobzilla has funded research that will culminate in a database of popular dry, wet, prescription raw food that have been analyzed for AGE levels. The higher the AGE level, the less healthy it is. This database will be available soon, but in the meantime, you can read more about it here.
So if feeding kibble is harmful, feed raw. If that isn't an option, home-cook. Anything is better than kibble and will result in a healthier and happier dog.