What is anal cancer?

Normally, the body's cells grow and divide to replace old or damaged cells in the body. This growth is highly regulated, and once enough cells are produced to replace the old, normal cells stop dividing. Tumors occur when there is an error in this regulation and cells continue to grow uncontrolled. Tumors can be benign or malignant. Although benign tumors may grow of
dysplasia is sometimes referred to as anal intraepithelial neoplasia (AIN) uncontrolled fashion sometimes, they do not spread beyond the body part where they started (metastasize) and do not invade surrounding tissues. Malignant tumors, however, will grow so that invade and damage other tissues around them. They can also spread to other parts of the body, usually through the bloodstream or lymphatic system through the lymph nodes, where they are. Over time, cells in a malignant tumor increasingly abnormal and appear less like normal cells. This change in the appearance of cancer cells is called the grade of the tumor and cancer cells are described as well differentiated, moderately differentiated, poorly differentiated or undifferentiated. well-differentiated cells are quite normal appearing and resemble normal cells from which they came. The cells are undifferentiated cells that have become so abnormal that often we can not say what types of cells began.

Anal cancer is a malignant tumor or the anal canal or anal margin. In the United States, 80% of anal cancers are squamous cell cancers,, resembling the cells found in the anal canal., This is not true in other parts of the world, however. In Japan, 80% of anal cancers are adenocarcinomas, resembling the glandular cells seen in the rectum. Cancers of the anal verge may be referred to as 'perianal skin cancer,' because usually behave more like skin cancers such as anal cancer. They may respond less to treatment than other forms of anal cancer. Perianal skin cancers represent about 25% of anal cancers. Occasionally, other types of cancer, including melanoma, Kaposi's sarcoma and lymphoma may develop in the anus. These other types of cancer are discussed separately, and will not be discussed further in this review.

Anal cancers often start as anal dysplasia. anal dysplasia is composed of cells from the anus that have abnormal changes, but show no evidence of invasion into surrounding tissues. The most severe form of anal dysplasia is called carcinoma in situ. In the case of carcinoma in situ, cells have become cancerous but have not begun to invade normal tissue yet. Over time, changes in anal dysplasia to the point where cells become invasive and increasing the capacity of metastasis, or break way to other parts of the body. Anal dysplasia sometimes referred to as anal intraepithelial neoplasia (AIN), or a 'pre-cancer.' When anal cancer spreads, it most commonly spreads through direct invasion into surrounding tissues or through the lymphatic system. The spread of anal cancer through the blood is less common, although it can occur.