Cancer diagnoses among Americans younger than 50 have risen for multiple cancer types, according to a new analysis using data on more than 2 million cancers diagnosed between 2010 and 2019. The study, led by researchers at the National Cancer Institute, examined cancer rates in people aged 15 to 49 and found that increases occurred for 14 of 33 cancer types in at least one younger age group.
In the researchers’ comparison, they evaluated cancer rates in 2019 against what would have been expected based on rates observed in 2010. Their results showed the largest increases were concentrated in breast, colorectal, kidney and uterine cancers, while the overall pattern was not uniform across all cancers.
Breast cancer accounted for the biggest share of the excess cancers, with about 4,800 additional cases in 2019 compared with expected rates based on 2010, according to the study. The analysis also estimated about 2,000 more colorectal cancers, 1,800 more kidney cancers and 1,200 additional uterine cancers relative to those expected rates.
The study found that the early-onset cancers it analyzed affected women more than men, with about 63% of early-onset cancers occurring among women. Researchers said the rising pattern “generally reflect[s] something profound going on,” and emphasized that additional work is needed to understand what is driving the changes.
Tim Rebbeck of the Dana-Farber Cancer Institute, who was not involved in the research, said the field needs to fund research that explains the patterns the study documents. The findings were published Thursday in Cancer Discovery, a journal of the American Association for Cancer Research.
Researchers also described potential explanations that could account for the observed increases. Meredith Shiels of the National Cancer Institute said several of the cancer types identified as increasing are known to be associated with excess body weight, and she pointed to increasing obesity as a leading hypothesis.
The researchers said advances in cancer detection and changes in screening guidelines could also be behind some diagnoses appearing at younger ages. They noted, however, that the large databases used for the analysis do not contain information on risk factors or access to care, which limits the ability to test specific causes directly.
Even with the increases highlighted in the analysis, the researchers said the pattern did not hold for every cancer. They reported that cancer rates in people under 50 were going down for more than a dozen cancer types, with the largest declines in lung and prostate cancers.
The researchers tied the lung cancer decline to decades-long reductions in cigarette smoking. For prostate cancer, the study said the drop likely corresponds to updated guidelines discouraging routine PSA testing in younger men because of concerns about overtreatment.