Yes, that IS how she got anal cancer.
Anal cancer is typically caused by Human papilloma virus (HPV), a sexually transmitted infection. Having anal sex – especially with many partners – puts the receiver at considerable risk of developing anal cancer:
• https://www.macmillan.org.uk/cancer-information-and-support/bowel-cancer/causes-and-risk-factors-of-anal-cancer
• https://www.cancer.org/cancer/types/anal-cancer/causes-risks-prevention/risk-factors.html
• https://www.mayoclinic.org/diseases-conditions/anal-cancer/symptoms-causes/syc-20354140
Red-blooded men strongly desire anal sex with hot women like Fawcett. Shame she ended up paying for her willingness to perform that most coveted of sex acts, with her life.