Upswing in Colorectal cancers in younger patients

Adult, non-graphic content below the fold. Proceed if you are inclined.

The CDC and World Health Organization are baffled by the rise in early-onset cancers of the lower bowel and rectum. Not only is it showing up in young(er) patients sooner than expected but the primary location is different than the historic norm.

Elevated risk in generations born since the 1950s, referred to as a birth cohort effect, is carried forward as individuals age and is already apparent in trends for people aged 50–64 years, which more closely resemble younger than older age groups since circa 2010 (Figures 5 and 6). Incidence (of colorectal cancer) is uniquely increasing for early onset disease in many high-income countries for reasons that remain unclear. Likely contributors include obesity, recently shown to be associated similarly with all major molecular subtypes of sporadic disease, and reduced dietary quality.    Source

Emphasis mine.

One cause that is tip-toed around is the normalization of "buggery" 

HPV infections are primarily spread by intimate contact. HPV is liked to cancers of the cervix, tongue, mouth, throat and anus. That last one, the anus, is very close to the rectum and colon.

Which brings us back to the changing location: The novel, early-onset cases are in the very lowest reaches of the bowel where it stops descending, turns inboard and then narrows to form the rectum. That is not where older-onset cases typically originate.

But it isn't just HPV. Bacterial infections are linked to increased cancer. Several causal routes have been identified. 

Bacterial infections are linked to local inflammation. Inflammation is liked to cancer. Bacterial infections kill cells and healing flips cellular "switches" to reproduction and sometimes the "off" switch fails and the cells keep dividing. 

Bacterial infections sometimes produce toxins and those toxins can damage DNA in human cells. 

Finally, some species of bacteria are capable of injecting DNA into other cells. That is one way that antibiotic resistance is passed from one species of bacteria to another. Those bacteria are not discriminating and can inject DNA into non-bacteria cells, it was one of the first methods of Genetic Engineering and used move genes from one species to another. Most of the genes are "junk" but some of them are able to hijack cellular processes.

The current CDC recommendations for "testing" of sexually active, gay men follows:

• HIV at least once a year;
• Syphilis;
• Hepatitis B;
• Hepatitis C based on risk factors;
• Chlamydia and gonorrhea of the rectum if you’ve had receptive anal sex (been a “bottom”) in the past year;
• Chlamydia and gonorrhea of the penis if you have had insertive anal sex (been a “top”) or received oral sex in the past year;
• Gonorrhea of the throat if you’ve performed oral sex (i.e., your mouth on your partner’s penis, vagina, or anus) in the past year;
• Sometimes, your healthcare provider may suggest a herpes test.

At the risk of editorializing:Buggery isn't what our bodies were "designed" for...whether by evolution or Divine intent. It is a misuse of the body, like using a Prius to pull stumps out of the fence-row. While you might "get away with it" if you do it once or twice, a heavy diet of the practice extracts a price.