How likely is it for an 18 year old to have cancer?

Younger age cancer: We are seeing a demographic shift now with many young patients presenting with cancers such as lung cancer, colorectal cancer, GI cancers, brain tumor, leukemias and lymphomas, testicular cancer, myelomas and head and neck cancer. In females breast and ovarian is also being shown now at young age. Cancer in an 18 year old would be at bottom of differential.

Vary: It depends on the family history and type of the cancer. Cancer can affect any ages starting from the infancy.