It's too early to jump to conclusions, it could be anything: A chemical used in bottles (for babies), traces of a chemical in infant formula, something in toothpaste, medicine, ect.
Given the rise in colon cancer in middle-aged adults, I suspect the two (teenage and middle aged colon cancer) are related.
The most ironic would be if it's caused by trace amounts of a fancy new pesticide used on a less-popular fruit or vegtable.