My grandfather, wife's grandfather, and mother all passed away from one form of cancer or another. We've had three horses we put down due to cancer (melanoma). No, I don't wonder. No, I don't search for some bogey man. The horses were grays. Grandparent's were old (in their eighties) and Mom had a very unhealthy lifestyle. Cancer is a name given to a collection of over 100 diseases. The biggest factors leading to a person, or animal, contracting cancer are age and genetic make-up (most animals don't live long enough for environmental factors to be a player). Some cancers are inherited. Others occur from genetic changes that occur over a lifetime. One of those is simply age itself and predisposition towards one form of cancer or another.
In all my years of work, I've only see two genuine cancer clusters. Both were mesothelioma. One case was the ship workers in Charleston. They would be enclosed in small spaces welding together parts of ships surrounded by asbestos dust. Another was a brake factory. The dust was so thick, you couldn't see from one end of the plant to the other. Only one person that worked there escaped mesothelioma. She was also the only nonsmoker.
That isn't to say there isn't a risk associated with certain chemicals. There are. But that risk is dependant on a pathway of exposure and dosage. In regards to 2,4-D, there is no evidence it causes cancer in any dosage. But the WHO wants to prove a negative (imposible). And because you can't, they say, maybe, possibly, 2,4-D does cause cancer. It is also possible that pigs do fly and a cow did jump over the moon.