Anal canal cancer

The anal canal is located at the end of the large intestine. The upper boundary is the tooth line and the lower boundary is the edge of the anus. The anal canal is close to the urethra and prostate in front of the male, and the uterus and vagina in the female; the tailbone is behind, surrounded by internal and external sphincter muscles. The true etiology of anal canal cancer is unknown, but studies have shown that it is caused by the out-of-control of multiple genes under the influence of multiple factors. In the past, long-term chronic stimuli such as anal fistula, genital warts, and immune disorders (such as Crohn disease) have been linked to the occurrence of anal canal cancer. In recent years, it has been found that human papillomavirus (HPV) is closely related to it, especially HPV-16, which is found in 50% to 80% of anal canal cancer cells.