More Americans are getting colon cancer, and at younger ages. Scientists aren't sure why.

Americans are getting cancer — colon cancer, breast cancer, cervical cancer and other types — at higher rates. And they're being diagnosed at younger ages, according to a study out Wednesday from the American Cancer Society.

Colorectal cancer, once the fourth-leading cause of cancer deaths for people younger than 50, has leaped up the list, becoming the leading cause for men and ranking second for women, the study, published in CA: A Cancer Journal for Clinicians, states. Cancer is the second-leading cause of death in U.S. adults, behind heart disease, according to the Centers for Disease Control and Prevention.

One bright spot in the report was that cancer deaths continued to decrease. But experts warned that given the rise in some of the most deadly forms of cancer being diagnosed, an increase in deaths could follow.