Some viruses are risk factors for cancer.
Certain strains of human papillomavirus (HPV), which are sexually transmitted, are the primary causes of cervical and anal cancer. Women who begin having sexual intercourse before age 17, or who have multiple sexual partners, are at greatest risk of HPV infection.
HPV may also be responsible for some cancers of the head and neck.
It's important to note that most people infected with HPV will not get cancer. Also, a vaccine is now available that can prevent infection with the strains of HPV that cause cervical cancer.
Hepatitis B and C
The hepatitis B and hepatitis C viruses are major causes of liver cancer worldwide. The viruses are transmitted through blood transfusions, injectable drug use, and unprotected sex. Vaccinations can protect against hepatitis B, but there is not yet a vaccine for hepatitis C.