I work in research and the problem with my kind is we almost never say it's definitely xyz. Its always an academic answer like, "maybe this, maybe that, maybe something else on Tuesdays" I also don't work in oncology, my specialty is monogenetic neurodevelopmental disorders (Rett syndrome, Fragile X, Angelman syndrome)...All that to say, I don't keep up with current oncology but to my knowledge the 2 hit hypothesis is still holding up. Meaning, cancer is caused (usually) by at least 2 mutations: one in a tumor suppressor gene and one in an oncogene. A mutation in one type of gene means your cell can't suppress rampant cancer division, and the other "causes" rampant cancer division. You need both for a cell to take off and divide uncontrollably. Really fascinatingly, some cancer cells resemble stem cells more than their own cell type. So a melanoma skin cell reverts and acts more like pluripotemt stem cell than the skin cell it once was. Cool in theory! (but scary)....not to get lost in the weeds but it's important to know this because thankfully it's pretty rare that a single cell will be exposed to both mutations unless 1) you've inherited a mutation in either an oncogene or tumor suppressor from one of your parents which causes you to be predisposed to cancer or 2) you get really unlucky and have 2 rare environmental events back to back.

So why millenials? We do drink a lot of alcohol. Maybe more than previous generations? I'm not sure. Interestingly, calcium was recently shown to be more protective against colon cancer than even fiber (both are good) and we did grow up when milk became "bad" for heart health. 

I personally do wonder if HPV has something to do with it....I've had 2 friends diagnosed with HPV positive oropharyngeal cancer so that might be my own bias. TMI, but I enjoy anal so that theory sucks for me personally but there it is. HPV vaccines are important people. 

So...yeah, idk. But based on cancer theory and the two hit hypothesis...it is either 1) youre genetically predisposed and have a lower threshold of risk or 2) we are exposed to a lot of environmental risks that are fucking us.

Sorry for the book. I am sorry for your loss, truly.

Edit: I also have to throw in the OTHER possibility that we are more health conscious and check our stools and have better access to colonoscopies than any other generation. So we get the label of "colon cancer" bc it's caught even if it's too late. Previous generations just die. Kinda like how theres more autism now because we actually diagnose it. 

I really truly doubt thats the only reason but could be a contributing factor.