Why is colorectal cancer killing so many young Americans?

James Van Der Beek, the actor who became a generational icon through his starring role in “Dawson’s Creek,” died at 48 following a battle with colorectal cancer.

His family announced that he passed peacefully, noting he met his final days “with courage, faith, and grace.” Yet Mr. Van Der Beek’s death underscores a disturbing trend that has alarmed oncologists and public health officials: colorectal cancer rates among younger adults have been rising sharply over the past two decades.

But there is one overlooked possible cause.