Anal cancers can also develop in a rare glandular tissue (adenocarcinoma). Less common lesions include small cell carcinomas, malignant lymphomas, sarcomas, melanomas or Paget's disease, an intraepithelial adenocarcinoma of the mucous or sweat glands. Melanomas have a poor prognosis , since they spread via the bloodstream.
Well-differentiated tumors have a more favorable prognosis than poorly differentiated tumors.
How It Spreads Anal tumors can extend directly into adjacent tissues, including the skin, sphincter muscle, or to local organs such as the prostate, bladder or vagina. Tumor cells can spread via the lymph system to lymph nodes in the groin (if the tumor is below the pectinate line) or to pelvic lymph nodes (if the tumor is above the pectinate line). Metastases can also travel through the bloodstream.
What Causes It Chronic irritation of the anus is a primary cause. People who get anal cancer usually have a history of risk factors , one of which may be related to the human papilloma virus , especially type 16, or the trauma of anal intercourse. It is believed that invasive cancer is preceded by premalignant changes known as intraepithelial neoplasia, which include proliferation of anal basal-like epithelial cells that replace the squamous cells.
