According to a new study published in the journal Cancer Discovery, the number of cases of many types of cancer is increasing in the US among people under 50, but the reasons for this remain unknown.

Researchers say that between 2010 and 2019, more than two million cases of early-onset cancer were diagnosed in the United States. The largest increases in early-onset cancer were found in women—in cases of breast cancer, colorectal cancer, kidney cancer, and uterine cancer. However, significant increases in other types of cancer—including pancreatic cancer, stomach cancer, and skin melanoma—were also observed in younger female patients.

The respective data came from an analysis of the US national cancer data, which was carried out by age group. The early-onset age groups included patients aged 15-29, 30-39, and 40-49.

Overall, the researchers found a significant increase in the occurrence of 14 types of cancer with at least one early-onset age group.

Nine of these cancers increased also in at least one older age group.

The authors of the study argue that while rates of some early-onset cancers have increased in the US in recent years, overall cancer deaths have not changed.

The lead author says the question of “why” remains unanswered, but this new study offers some clues.

According to lead author, these results suggest that there may be risk factors that influence cancer development in different age groups, or advances in screening or imaging technology that enable cancer to be detected more often than in the past.