NEW YORK — New guidelines released Wednesday recommend most U.S. adults start colon cancer screening earlier, at age 45 instead of 50. The American Cancer Society's advice puts it out of sync with guidelines from an influential government advisory group, which kept the age at 50 in an update two years ago.

Cancer society officials acknowledge the shift to 45 could cause confusion for doctors and patients but felt strongly that they needed to act now. The advocacy group was influenced by its study, published last year, that found rising rates of colon cancer and deaths in people younger than 50. Experts aren't sure why there has been a 50 percent increase in cases since 1994.

Forty-seven-year-old Sandy Kyrkostas was one such patient who was diagnosed with stage 4 colon cancer that had spread to his liver. Two different doctors told him he had months to live.

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"When they tell you and your wife when you have two young children, 'get your life in order' ... that's a scary point," Kyrkostas told CBS News.

While cases like his have risen dramatically in the past two decades, colorectal cancer rates have steadily declined in people over 55 because of screening. Colon cancer is typically considered more treatable if it is caught early.

"If we can identify patients with early onset colon cancer earlier we have a better chance of curing them," said Dr. Manish Shah, an oncologist at New York Presbyterian Weill Cornell Medical Center.

Shah was Kyrkostas' third doctor and the first to give him hope. After four years of treatment, including 12 rounds of chemotherapy and nine surgeries, he is now disease-free.

The new guidelines are for men and women ages 45 to 75 of average risk for colon cancer. CBS News chief medical correspondent Dr. Jon LaPook, who is a gastroenterologist, explains that most people will fall into that category unless they have specific high-risk factors.

"A high risk would be somebody with a family history of colon cancer, or somebody who has a certain genetic condition, or you have a certain kind of inflammatory bowel disease," he said on "CBS This Morning." "Those people need to be tested even earlier -- say at 40 or even earlier. That's something you specifically talk about with your doctor."

The American Cancer Society endorses six kinds of screening exams, from inexpensive take-home stool tests performed every year to colonoscopies done every 10 years.

"All of these tests are good tests, and the choice should be offered to patients," said the cancer society's Dr. Rich Wender. "The best test is the test that gets done."

The same tests are recommended by the U.S. Preventive Services Task Force, a panel that reviews evidence and issues advice for a variety of screenings and treatments. It updated its colon cancer guidelines in 2016 and its next review isn't expected until around 2021.

That panel's recommendations drive what screening is covered by insurance under the Affordable Care Act, although 20 states have laws that link coverage to the cancer society guidelines. It's not uncommon for groups to have slightly different guidelines although those for colon cancer have been about the same for decades.

Most colon cancer occurs in adults 55 and older, and the good news is rates of cases and deaths have been falling for decades. Colon cancer, combined with rectal cancer, is the second leading cause of cancer death in the U.S. This year, more than 140,000 Americans are expected to be diagnosed with it, and about 50,000 will die from it.

Medical experts are still trying to figure out what's behind the dramatic rise in cases among adults in the younger age group.

"That is the million-dollar question," LaPook said. "Some people wonder, is it obesity? Is it lack of exercise? Diet? Something in the environment? What I think is really interesting is the possibility it's the microbiome -- so the trillions of bacteria that are in our gut. And there's one to two thousand different species, and it turns out that certain of those species are linked to a higher risk of colon cancer. And when you think about it, we have been changing our microbiome -- we take antibiotics, our diet has changed -- and one of the theories is that we're messing up our microbiome and increasing the risk that way. That's just the theory."

Doctors will probably look to specialty medical societies to sort out the different guidelines, said Dr. Marcus Plescia, of the Association of State and Territorial Health Officials. But it may take a little while before they offer clear advice.

Some experts have worried about pre-50 risks of colon cancer in some racial and ethnic groups, and at least one specialty society for gastroenterologists has urged screening of black adults starting at age 45.

Others argue that instead of lowering the age for routine screening, more effort should be put into getting more people tested. Only about two-thirds of people 50 and older have been following screening guidelines.

"It's hard enough to get people to do it at all," Plescia noted.

Dr. Andrew Wolf, the lead author of the latest guidelines, said they considered and rejected that reasoning.

"We should be able to do both," said Wolf, a University of Virginia internist.