(CNN) Kim Newcomer was knowledgeable about colon cancer; her father was diagnosed with the disease at age 46, she said. So after returning from a trip to the Dominican Republic in 2008, when she complained of constipation to her primary care physician, she was surprised that her doctor sent her home with laxatives instead of testing her for the cancer.
"I spent the next few months just going to the doctor, trying to get a diagnosis. In the first four months, I probably saw six different doctors," Newcomer said. "They couldn't find anything wrong with me even though I stressed that I had a family history of colorectal cancer. They thought I was just too young for it."
In the months following, Newcomer said, she developed a persistent cough and underwent a chest x-ray. The x-ray revealed lesions in her lungs and one breast.
Once the tumors in her breast and lungs were biopsied and analyzed, doctors confirmed what Newcomer had suspected all along.
"Eleven months after I had first complained of symptoms, I was diagnosed with stage-4 colorectal cancer," Newcomer said. She was 35 at the time.
Newcomer's initial misdiagnosis demonstrates a growing problem among younger colorectal cancer patients, according to research to be presented at the American Association for Cancer Research's annual meeting in Atlanta on Tuesday.
The research surveyed 1,195 colorectal cancer patients and survivors ages 20 to 49, mostly from the United States. Newcomer was one of them.
The research found that the majority of survey respondents, 57%, were diagnosed between the ages of 40 and 49; a third were diagnosed between the ages of 30 and 39; about 10% were diagnosed before age 30.
Although most colorectal cancer patients older than 50 are diagnosed in the early stages of disease, the new research revealed that most of the younger patients and survivors in the study, 71%, said they were diagnosed at the advanced stages of 3 and 4.
That finding suggests that with no screening and awareness of the possibility of colorectal cancer at these ages, signs of their cancer may have gone missed in its early stages.
The survey responses also showed that most of the patients and survivors, 63%, waited three to 12 months before visiting their doctors for symptoms, because they didn't recognize their symptoms as cancer-related.
Also, 67% of the respondents said they saw at least two physicians before being diagnosed correctly with colorectal cancer, which includes both colon and rectal cancers.
"It's an overlooked population because they're younger and usually tend to be healthy," said Dr. Ronit Yarden, lead author of the research and director of medical affairs at the nonprofit Colorectal Cancer Alliance, a patient advocacy organization in Washington.
"It's most important that people know the symptoms," she said.
Limitations of the research included that the survey responses were self-reported, and more research is needed to determine whether similar findings would emerge among a larger sample of patients compared with older patients.
"It's still a rare thing for younger people to get colon cancer," said Dr. Paul Oberstein, a medical oncologist and director of the Gastrointestinal Medical Oncology Program at NYU Langone's Perlmutter Cancer Center in New York, who was not involved in the new research.
"But it does happen, and I think for people who have signs of it -- constipation, rectal bleeding or trouble going to the bathroom -- they should get evaluated for cancer, among other conditions," he said.
Symptoms of colorectal cancer include diarrhea or constipation; feeling that your bowel does not empty completely; blood in your stool; frequent gas pains or cramps; weight loss with no known reason; fatigue, and nausea or vomiting.
The American Cancer Society updated its colorectal cancer screening guidelines last year to recommend that adults at average risk get screened starting at age 45 instead of 50, as previously advised. Screening options can range from getting a highly sensitive fecal test annually to undergoing colonoscopy every 10 years.
Those at higher risk include African Americans, Alaska Natives and people with a family history or a personal history of colon or rectal polyps; such risk factors could require screening at an earlier age.
"What's really important is that people who have a family history of colon cancer -- being any first-degree relative who had colon cancer at any age -- that person should get screened at age 40 or 10 years before the family member's diagnosis," said Oberstein, who was not involved in the guidelines.
"So if your father had it at 45, get screened at 35," she said.
The updated guidelines, published in CA: A Cancer Journal for Clinicians, stated that average-risk adults in good health with a life expectancy of more than 10 years should continue colorectal cancer screening through the age of 75.
Colorectal cancer is the third most common cause of cancer-related deaths globally, according to the World Health Organization.
In the United States, colorectal cancer is the second-leading cause of cancer-related deaths among cancers that affect both men and women, according to the Centers for Disease Control and Prevention.
Previous studies have suggested that rates of colorectal cancer deaths are climbing among adults younger than 55 in the United States.
After declining overall from 1970 to 2004, colon and rectal cancer mortality rates among 20- to 54-year-olds in the United States increased by 1% each year from 2004 to 2014, according to a 2017 study in the medical journal JAMA.
As for Newcomer, by 2012, she no longer showed evidence of disease and has been a cancer survivor ever since, but she said that her story could help raise awareness about how colorectal cancer easily can go overlooked in younger adults.
"I still have long-term effects. So I have a hard time walking; I have a hard time with neuropathy with my hands and feet. I have zero sexual function due to radiation and chemotherapy treatments," said Newcomer, now 45 and living in Arizona, who runs the Never Too Young outreach program at the Colorectal Cancer Alliance.
"It's so important to get this information out to other patients and survivors," she said. "The bigger issue is, how do we educate young people and medical professionals on the increase of young-onset colorectal cancer?"
While colorectal cancer remains much more common after age 50, "we are seeing an uptick of younger people being diagnosed with colon cancer," said Dr. Nilofer Azad, associate professor of oncology at the Johns Hopkins Kimmel Cancer Center in Baltimore and a member of the Stand Up to Cancer Colorectal Cancer Dream Team, who was not involved in the new research.
Specifically, colon cancer incidence rates increased by 1% to 2.4% annually since the mid-1980s in adults 20 to 39 and by 0.5% to 1.3% since the mid-1990s in adults 40 to 54, according to a study published in the Journal of the National Cancer Institute in 2017.
Though those incidence rates in younger adults still remain small, the study found that consequently, someone born circa 1990 would now have double the risk of colon cancer and quadruple the risk of rectal cancer at the same age than if they been born circa 1950.
Anecdotally, Azad said, she has seen more colorectal cancer patients under the age of 50 -- including in their 20s and 30s -- over the past few years, whereas that was very uncommon before.
"But that's not real data. It's one doctor's experience, and I work in a larger center where people come to seek out second and third opinions," Azad said.
Often, when colorectal cancer symptoms emerge in younger adults, a physician might refer that patient to other doctors to get different opinions.
"If you are feeling worried about something and your doctor is not worried but your symptoms continue, it's always reasonable to get a second opinion. ... It's always good to be an advocate for yourself," Azad said.
"When you have symptoms that are consistent with a diagnosis of colorectal cancer, you should be evaluated the same way a person would be evaluated if they were 30 years older," she said. "The default should be to rule out serious conditions, including cancer, rather than making assumptions that something is not cancer or benign."