No cancer is not a sexual disease but yet a lot of std's have been linked to cancer HPV ( which exist at least 40 different types of hpv is one of them)
I found this article and I hope it could be useful
http://www.bbc.co.uk/news/health-23374920
I believe what makes an appointment risky is the type of sex both engage not the gender.
I can't speak for all the transgenders , I obviously never engaged unprotected sex with a client and the reason why i have my std certificates is only becouse statistically the lgbts and the sex workers have always been linked when it comes to sexual transmitted infections . That turns off a lot of punters so they can feel safer with an escort who is careful with her health. Anyways its the girl's ( ts, gg, or any sex worker's prerogative have their sti certificates .