Hi Robin,
Sorry to hear about your sister's diagnosis. I hope that she is being treated at a comprehensive cancer center.

As a starting point for learning more, I would suggest searching the OCF web site for 'HPV'. There is a lot of good information available right on the web site.

For example, one section 'HPV Causes Oral Cancer' (http://www.oralcancerfoundation.org/facts/hpv_reports.htm) lists a number of studies related to this virus and its relation to oral cancer. Hope this helps.
Best, Sheldon