Michael Douglas is a well known actor, and his fight with head & neck cancer has been the subject of much public attention. Adding to that attention this week, he mentioned that his cancer was caused by HPV (Human Papilloma Virus) and as such has a very good prognosis. In addition, he noted the connection between exposure of this virus and sexual activity, particularly oral sex.
This connection has been well-documented and is often presumed to be the exposure that adds the final element in causing those head & neck cancers that have the HPV genetics expressed in the cancer tissue. That said, the traditional risk factors of tobacco and alcohol use cannot be dismissed as additive agents in these cancers and as being significant risk factors
It is possible that the exposure to the HPV virus was other than of a sexual nature, because the virus can be present in oral secretions as well and could be transmitted that way, but the generally consensus is that this is an STD related cancer.