Generation X and Millennials have a higher risk of 17 types of cancer, study finds

As cancer cases rise among young adults in the United States, a new study has identified 17 types of cancer that appear to be more common in Generation X and Millennials than in older age groups.

Among adults born between 1920 and 1990, there is a significant difference between each generation in the incidence of cancer rates and types, including breast, colon and rectal, pancreatic and uterine cancer, according to the study published Wednesday (31) in the journal The Lancet Public Health.

“Uterine cancer is one that really stands out, where we see tremendous increases. It has about a 169 percent higher incidence rate if you were born in the 1990s compared to someone born in the 1950s — and that’s for people of the same age. Someone born in the 1950s when they were in their 30s or 40s saw a different incidence rate compared to someone born in the 1990s in their 30s or 40s,” says William Dahut, chief scientific officer of the American Cancer Society, whose colleagues were authors of the new study.

“What’s a little different about this paper is that it includes a broader range of cancers,” he says. “In fact, it looked at 34 different types of cancer, and in 17 of them we saw an increase in incidence, and in five of them we saw an increase in mortality in young adults under 50.”

These 17 types of cancer are:

• Gastric cardia cancer;
• Small intestine;
• Estrogen receptor-positive breast cancer;
• Ovary;
• Liver and intrahepatic bile duct in women;
• Non-HPV-associated mouth and pharynx cancers in women;
• Anus;
• Colon and rectum;
• Uterine body;
• Gallbladder and other bile ducts;
• Kidney and renal pelvis;
• Pancreas;
• Myeloma;
• Non-cardia gastric cancer;
• Testicle;
• Leukemia;
• Kaposi’s sarcoma, which affects the lining of blood and lymph vessels, in men.

The researchers, from the American Cancer Society and the University of Calgary in Canada, analyzed data from more than 23 million patients diagnosed with 34 types of cancer and more than 7 million people who died from 25 types of cancer.

The data, which came from the American Association of Central Cancer Registries and the National Center for Health Statistics, included adults aged 25 to 84 from January 2000 to December 2019. The researchers calculated cancer incidence rates and cancer death rates by birth year, separated by five-year intervals, from 1920 to 1990.

The researchers found that incidence rates increased with each successive cohort born since about 1920 for eight of the 34 cancers. The rate was about two to three times higher among those born in 1990 than among those born in 1955 for pancreatic, kidney and small bowel cancers in both men and women, and for liver cancer in women.

Among cancer types, the increase in incidence rate among people born in 1990 ranged from 12% higher for ovarian cancer to 169% higher for uterine corpus cancer compared with birth cohorts that had the lowest incidence rates.

The rising incidence of certain cancers among young adults nationally suggests that “this increase is potentially due to changes in environment or lifestyle,” says Andrea Cercek, a gastrointestinal medical oncologist and co-director of the Center for Young-Onset Colorectal and Gastrointestinal Cancer at Memorial Sloan Kettering Cancer Center, in an email.

“What this study shows is that some cancers that were previously not prevalent in young adults are now increasing in incidence,” says Cercek, who was not involved in the new research. “It is not known why these cancers, such as estrogen receptor-positive gastrointestinal, gynecologic and breast cancers, are increasing in incidence in young adults, but we believe this increase is likely due to early exposure to an environmental factor or factors.”

The researchers found that 10 of the 17 cancers with increased incidence in younger cohorts were linked to obesity: colon and rectum, kidney and renal pelvis, gallbladder and other bile ducts, uterine body, pancreas, gastric cardia, estrogen receptor-positive breast cancer, ovary, myeloma, and liver and bile duct.

Because cancer takes time to develop, obesity-related cancer in a young adult may be linked to childhood health.

“If people are developing cancer at an earlier age, that means their exposure—whether it’s environmental, climate, dietary, or whatever—occurred at a younger age as well,” Dahut says. “If you get cancer in your 30s or 20s, then your teens, or even earlier, were probably the time when you had that exposure or the triggering event.”

The researchers also found that cancer death rates increased in successively younger generations, along with incidence rates for liver cancer in women, uterine corpus, gallbladder, testicular, and colon and rectal cancers.

The new study brought some good news: Cancers that are not increasing — and are even declining in younger generations — include those related to tobacco, such as lung cancer, and HPV infections, such as cervical cancer.

The “accelerated decline” in cervical cancer incidence trends shows the effectiveness of HPV vaccination among women born around 1990, who were about 16 when the vaccine was approved in the United States, the study found. And the downward trends for tobacco-related cancers reflect a rapid decline in smoking prevalence among younger generations.

“These findings add to growing evidence of increased cancer risk in post-Baby Boomer generations, expanding previous findings of early-onset colorectal cancer and some obesity-associated cancers to encompass a broader range of cancer types,” said Hyuna Sung, lead author of the study and senior principal scientist for surveillance and health equity science at the American Cancer Society, in a press release.

“Birth cohorts, groups of people classified by birth year, share unique social, economic, political and climatic environments that affect their exposure to cancer risk factors during their crucial developmental years,” he says. “Although we have identified cancer trends associated with birth years, we still do not have a clear explanation for why these rates are increasing.”

A growing trend towards earlier screening

Several factors — including dietary changes, declining physical activity levels, rising rates of childhood obesity and the increasing use of more advanced diagnostic tests — are likely behind the rising incidence of cancer among younger age groups, according to Ernest Hawk, chairman of the Division of Cancer Prevention and Population Sciences at the University of Texas MD Anderson Cancer Center, who was not involved in the study.

“Particularly because a number of these cancers that we know are related to obesity, this may be the most likely of the possible culprits that have been discussed so far,” says Hawk.

However, health care professionals in the United States have the tools to diagnose many of these cancers at earlier stages, leading to greater chances of survival, Hawk added, and the new findings indicate that we may need to start screening earlier for some cancers.

“This has already happened for both breast cancer screening and colon cancer screening. For both, in just the last five years, we’ve lowered the age to start screening in the general average-risk population,” Hawk says. “So the downward migration in the age to start screening has already started to move in that direction for some cancers, partly for that same reason.”

He was referring to screening guidelines from the US Preventive Services Task Force (USPSTF), a voluntary panel of independent medical experts whose recommendations help guide doctors’ decisions and influence insurance plans.

In 2021, the USPSTF lowered the recommended age to start screening adults at average risk for colorectal cancer from 50 to 45. This guidance is for those who have no symptoms and who do not have a diagnosis of colorectal cancer, a history of polyps in the colon or rectum, or a personal or family history of genetic disorders that put them at higher risk.

In May, the task force updated its breast cancer screening recommendations for average-risk adults, advising

Women should have a mammogram every two years, starting at age 40 and continuing through age 74. The previous recommendation called for biennial mammograms starting at age 50, and the decision for women to get screened at age 40 “should be an individual decision.” The new guidelines are more in line with those of other groups, such as the American Cancer Society.

Overall, “the findings of increased cancer incidence in recent birth cohorts for 17 cancer types have important public health implications,” the researchers wrote in their study. “Improving awareness among health care professionals and the general public about the signs and symptoms of cancer among young adults is crucial for early detection and treatment.”

Dahut explains that signs and symptoms of most types of cancer can include abnormal bleeding, as blood in the stool can be a sign of colorectal cancer or unusual vaginal bleeding can be a symptom of uterine cancer.

Other symptoms to look out for include “persistent, dull pain that you’ve never had before — that’s something people should at least get medical advice about,” says Dahut.

“Any lymph nodes or abnormal growths that are not explained,” he added. “Fatigue, weight loss — those tend to be with much more advanced cancer, and I think at that point, most people tend to go to someone because they feel sick.”

Seeking medical care remains important, as Dahut says, “delaying a diagnosis for six, eight, 10 or 12 months before seeing a doctor can definitely lead to more advanced disease and a worse outcome.”

Cancer has been affecting more people in their 30s and 40s; understand