What we thought we knew about colorectal cancer is changing: It’s no longer confined to older adults, and it no longer follows a predictable pattern.
While men and women are diagnosed at similar rates, emerging research suggests important differences in how the disease shows up — and why it may be harder to catch in younger patients, particularly women.
“There's kind of a fable out there that colorectal cancer is an old man’s disease,” says Folasade May, MD, Ph.D., an associate professor of medicine at UCLA. “We have to really fight that and recognize these trends — it's no longer an old person’s disease. And it is certainly not only a man’s disease.”
So is this a gender divide — or something bigger? Here’s what the data actually shows, and why diagnosis can be especially complicated.
What’s actually driving the shift — gender, age, or both?
The discrepancy isn't just in the rate of occurrence — it’s also caused by tumor location.
A 2020 study published in Scientific Reports found that although women are diagnosed with colorectal cancer slightly less often than men overall, they are more likely to develop tumors in the proximal (or right side) of the colon. And that location matters: The right side of the colon is wider, and stool in that part of the intestine is still relatively liquid. As a result, tumors can grow for longer without causing obstruction or obvious bleeding.
Rather than producing dramatic warning signs, right-sided cancers often present more subtly — such as iron-deficiency anemia from slow internal blood loss, fatigue, or vague abdominal discomfort. Those symptoms are easy to rationalize, especially in younger women. Fatigue gets blamed on work or parenting. Bloating gets chalked up to hormones. Mild abdominal pain gets dismissed as IBS.
By contrast, tumors in the distal or left side of the colon are more likely to cause visible rectal bleeding or noticeable changes in bowel habits earlier, partly because the passageway is narrower and stool is more formed.
That anatomical difference may help explain why right-sided tumors are often diagnosed at a later stage — and why they’re associated with poorer outcomes, including roughly a 20 percent higher risk of death compared with left-sided cancers.
But experts caution against framing the disease primarily through the gender divide. “It’s not so much a gender difference,” says Dr. May, who co-authored a 2024 study examining generational trends in colorectal cancer. “The bigger change we’re seeing is by age.”
In that study, researchers found that among adults ages 50 to 59, cancers in the proximal (right) colon, distal (left) colon, and rectum occurred at roughly similar rates in the early 1990s. Since then, the pattern has shifted: rectal cancer rates have steadily increased — rising about 0.7 percent per year — while cancers in both the right and left colon have slightly declined.
That shift is even more pronounced in younger adults. In patients diagnosed before 50, tumors are more likely to appear on the left side of the colon — particularly in the rectum and sigmoid colon — rather than on the right. Several large analyses of early-onset colorectal cancer have found this same pattern, with cancers in younger patients disproportionately arising in the rectum and distal colon compared with older adults.
Right-sided tumors still occur, Dr. May notes, but the broader pattern suggests that age — and possibly shared generational exposures — is reshaping not just who develops colorectal cancer, but where it begins.
Researchers describe this generational shift as a “birth cohort effect,” meaning risk climbs with each successive generation — a pattern that typically signals shared exposures rather than inherited genetics, says Kimmie Ng, MD, a professor of medicine at Harvard Medical School. She adds that the leading hypotheses include sedentary behavior, ultra-processed diets, and other modern lifestyle changes. Scientists are also investigating broader forces, from pollution to microplastics. Still, no single driver has been definitively identified.
As researchers debate what’s driving the rise, one undeniable pattern is that symptoms in younger women are often misread or minimized.
Are women’s GI symptoms more likely to be dismissed?
In younger women, colorectal cancer doesn’t always present with the classic red flags doctors were trained to look for, such as unexplained weight loss, persistent rectal bleeding, or a sustained change in bowel behavior.
Instead, symptoms like bloating, pelvic pain, fatigue, or subtle shifts in bowel patterns can blur into the background of menstrual cycles; pregnancy; IBS; hemorrhoids; or common gynecologic conditions like endometriosis, ovarian cysts, or fibroids. Life stages such as pregnancy and perimenopause can further cloud the picture, as exhaustion and abdominal discomfort are often attributed to hormonal shifts or postpartum recovery.
“Colorectal cancer in young women can present quite differently,” Dr. May says. “Symptoms are often mistaken for benign or gynecologic conditions and ignored by the patient or the doctor.”
Iron-deficiency anemia is one of the clearest examples of how easily cancer symptoms can be attributed to something else in women. “A lot of times women will have low iron levels, and doctors will say, ‘Oh, it must be your menses or your diet,’” Dr. May explains. “Those are factors men don’t have. When anemia is automatically attributed to something gynecologic, cancers can grow for a long time before they’re actually investigated.”
Dr. Ng adds that unexplained anemia should always prompt further evaluation. “If someone develops anemia without a clear reason, that needs to be worked up,” she says. “Anemia in a man doesn’t have an alternative explanation like menses, so it may be investigated more urgently.”
There’s one symptom doctors say should never be ignored: blood in the stool. While hemorrhoids are common and benign causes are far more likely, bleeding that persists or worsens shouldn’t be dismissed and warrants evaluation with a colonoscopy.
Beyond obvious bleeding, changes in your normal patterns also matter.
Women should pay attention to what’s typical for their own bodies throughout their cycles. “Knowing what your normal bowel pattern is — and recognizing when something changes — is really important,” Dr. Ng says. “If there’s new constipation, new diarrhea, or thinning of the stool that’s different from your usual pattern and it doesn’t resolve, you need to see your doctor.”
What gastroenterologists want women to know
If something feels off, say so. And if you don’t feel heard the first time, say it again.
“Women should definitely ask their primary care doctor about their symptoms and ask for an explanation,” Dr. May says. If the answer doesn’t sit right — or if symptoms persist — she recommends seeking a referral to a gastroenterologist, the specialist who evaluates digestive conditions and performs colonoscopies.
If symptoms are being attributed to hormones, periods, or a gynecologic issue, it’s reasonable to ask follow-up questions there, too. “You want to make sure it truly is a gynecologic issue if that’s what’s being suggested,” she adds.
Both doctors say second opinions shouldn’t feel dramatic — they should feel normal. “If your primary care doctor is not supportive of that plan and you feel your symptoms are still unexplained, you should see a second doctor,” Dr. May says.
But this isn’t just about patients pushing harder. Medicine itself is adjusting to a new reality.
In 2021, the U.S. Preventive Services Task Force lowered the recommended screening age from 50 to 45 — a major shift driven by rising rates in younger adults, including women in their thirties and forties. The change reflects what many gastroenterologists had already begun seeing in their clinics.
“There’s still a relative lack of awareness that colorectal cancer can happen in a young and otherwise healthy person,” Ng says.
For decades, the disease was framed as something that primarily affected older men. “When I was in medical school — which wasn’t that long ago — we were taught that you only worry about colorectal cancer in someone in their 70s or 80s,” Dr. May tells us. “Relearning needs to happen so that doctors have a high level of suspicion for colorectal cancer in a young woman.”
