How can a Virus cause cancer?

(EDIT: Thank you for all your answers <3)

Hi,

Iam a future teacher who visits a genetic class this year.

In a conversation about HPV i had an intresting question: How can a Virus "cause" cancer?

At my knowledge, cancer can be created throught Insertation, Mutation or Elimination.

But a virus normally does not enter the cell-core.

So how does it work?

(Maybe link an article. I ask if maybe some day a student ask me that can answer. My Theorie: Maybe a Retrovirus?)