A study published in JAMA Network Open reveals that rates of cancer increased by 30% from 1973 to 2015 in adolescents and young adults (AYAs) (persons aged 15–39 years) in the United States, according to a review of almost a half million cases in the National Institutes of Health’s Surveillance, Epidemiology, and End Results database.

There was an annual increase of 0.537 new cases per 100,000 people, from 57.2 cases per 100,000 in 1973 to 74.2 in 2015.

Kidney carcinoma led with the highest rate increase. There were also marked increases in thyroid and colorectal carcinoma, germ cell and trophoblastic neoplasms, and melanoma, among others.

The reasons for the increases are unclear, but environmental and dietary factors, increasing obesity, and changing screening practices are likely in play, the authors comment. In addition, “cancer screening and overdiagnosis are thought to account for much of the increasing rates of thyroid and kidney carcinoma, among others,” they add.

Read more about the study here.