In a new study, researchers found that colorectal cancer rates among US adults have a 46% increase in new diagnoses from ages 49 to 50.
They found that almost 93% of the cases discovered at age 50 were invasive, meaning that most would require more aggressive treatment including surgery and likely existed for some time before diagnosis.
The finding shows that many latent cases are likely going undiagnosed until routine screenings begin at 50.
The research was conducted by a team at Tulane University School of Medicine and elsewhere.
Colorectal cancer is the second leading cause of cancer deaths in the US.
As rates for younger adults continue to rise, considerable debate exists about whether to lower the age for recommended screenings.
In 2018, the American Cancer Society called for routine screenings to start at 45.
However, the US Preventive Services Task Force, which sets federal screenings standards, currently recommends average-risk screening begin at age 50.
The agency is studying the issue to determine whether changes will improve outcomes.
Those against beginning screenings at age 45 have argued that incidence rates in people aged 45 to 49 years remain relatively low compared to those aged 50 to 54 years.
The researchers suspect some may underestimate the risks for those in their mid-to-late 40s because incident data for those age ranges would likely only include cases caught because they presented symptoms and/or have a family history of cancer, in contrast to those 50 and older who have cancers also detected due to screening.
To assess this, they examined colorectal cancer incidence rates in one-year increments between the ages of 30 to 60 from the year 2000 to 2015.
They suspected that if they found many undetected asymptomatic cases of the disease they would also see a marked increase in cases between 49 and 50 when screenings begin.
The findings showed a steep increase from 34.9 diagnoses per 100,000 people at age 49 to 51 cases per 100,000 at age 50.
The findings also showed sharp increases in both men (52.9%) and women (39.1%), in white (46.2%) and black (47.3%) populations in the colon (51.4%) and rectal (37.6%) cancers in this one-year age transition.
Researchers also examined the stage at which doctors caught the cancers and found a spike in localized and regional cancers, requiring surgery and possibly chemotherapy and radiation treatment.
The study adds fuel to the debate about whether screenings should begin at age 45.
The team says the combined burden of undetected and detected early-onset colorectal cancer cases for those 45 to 49 may actually approach that of individuals in their early 50s.
One author of the study is Jordan Karlitz, an associate clinical professor of medicine.
The study is published in JAMA Network Open.
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