Oral sex leads to head cancer?

What? I'm total piqued by this research. How can the two relate?

The number of serious head and neck cancers linked to a virus spread by oral sex is rising rapidly and suggests boys as well as girls should be offered protection through vaccination, doctors said on Friday.

Despite an overall slight decline in most head and neck cancers in recent years, cases of a particular form called oropharyngeal squamous cell carcinoma (OSCC) have increased sharply, particularly in the developed world.

Read on here from Sydney Morning Herald.

Totally strange!