Рак анального канала: причины, симптомы и профилактика

cancer of the colon or rectum

Symptoms of anal cancer can include pain or pressure in the anus or rectum, a change in bowel habits, a lump near the anus, rectal bleeding, itching or discharge. Bleeding may be severe.

Human papillomavirus: Examination of squamous cell carcinoma tumor tissues from patients in Denmark and Sweden showed a high proportion of anal cancers to be positive for the types of HPV that are also associated with high risk of cervical cancer. In another study done, high risk types of HPV, notably HPV 16, were detected in 84 percent of anal cancer specimens examined. Based on the study in Denmark and Sweden, Parkin estimated that 90% of anal cancers are attributable to HPV. Sexual activity: Due to increased risk of exposure to HPV, having multiple sex partners and receptive anal intercourse greatly increases the likelihood of developing anal cancer, for men and women. Smoking: Current smokers are several times more likely to develop anal cancer compared with nonsmokers. Cloacogenic. Cloacogenic carcinoma is a rare tumor of the anorectal region originating from a persistent remnant of the cloacal membrane of the embryo. The tumor accounts for 2–3% of anorectal carcinomas and occurs more than twice as often in women.

Most anal cancers are squamous cell carcinomas (epidermoid carcinomas), that arises near the squamocolumnar junction. It may be keratinizing (basaloid) or non keratinizing (cloacogenic). Other types of anal cancer are adenocarcinoma, lymphoma, sarcoma or melanoma.

Since many, if not most, anal cancers derive from HPV infections, and since the HPV vaccine before exposure to HPV prevents infection by some strains of the virus and has been shown to reduce the incidence of potentially precancerous lesions, scientists surmise that HPV vaccination may reduce the incidence of anal cancer. The efficacy of the vaccine against HPV types 16 and 18 in naive women ≤26 years old has been shown to be between 91 100% but is lower when individuals are vaccinated irrespective of baseline HPV infection at 76%. In 2010, Gardasil was approved in the US to prevent anal cancer and pre cancerous lesions in males and females aged 9 to 26 years. The vaccine has been used before to help prevent cervical, vulvar, and vaginal cancer, and associated lesions caused by HPV types 6, 11, 16, and 18 in women.

As the incidence of anal cancer has increased in recent years, screening and early detection of anal intraepithelial neoplasia (AIN) has become a necessity in patients at risk. This screening detects premalignant lesions, which are highly prevalents, and improves the staging of lesions after treatment. Anal Pap smears similar to those used in cervical cancer screening have been studied for early detection of anal cancer in high risk individuals. In 2011, an HIV clinic implemented a program to enhance access to anal cancer screening for HIV positive men. Nurse practitioners perform anal Papanicolaou screening, and men with abnormal results receive further evaluation with high resolution anoscopy. The program has helped identify many precancerous growths, allowing them to be safely removed. A similar study was performed in women with a history of cervical cancer or high grade cervical intraepithelial neoplasia. More than 30% had abnormal anal Pap smears and one third of those already had anal intraepithelial neoplasia.

Localised disease (carcinoma in situ) and the precursor condition, anal intraepithelial neoplasia (anal dysplasia or AIN) can be ablated with minimally invasive methods such as infrared photocoagulation. Previously, anal cancer was treated with surgery, and in early stage disease (i. e., localised cancer of the anus without metastasis to the inguinal lymph nodes), surgery is often curative. The difficulty with surgery has been the necessity of removing the internal and external anal sphincter, with concomitant fecal incontinence. For this reason, many patients with anal cancer have required permanent colostomies. This "combined modality" approach has led to the increased preservation of an intact anal sphincter, and therefore improved quality of life after definitive treatment. Survival and cure rates are excellent, and many patients are left with a functional sphincter. Some patients have fecal incontinence after combined chemotherapy and radiation. Biopsies to document disease regression after chemotherapy and radiation were commonly advised, but are not as frequent any longer. Current chemotherapy consists of continuous infusion 5 FU over four days with bolus mitomycin given concurrently with radiation. 5 FU and cisplatin are recommended for metastatic anal cancer.

10 to 20% of patients treated for anal cancer will develop distant metastatic disease following treatment. Metastatic or recurrent anal cancer is difficult to treat, and usually requires chemotherapy. Radiation is also employed to palliate specific locations of disease that may be causing symptoms. Chemotherapy commonly used is similar to other squamous cell epithelial neoplasms, such as platinum analogues, anthracyclines such as doxorubicin, and antimetabolites such as 5 FU and capecitabine. JD Hainsworth developed a protocol that includes Taxol and Carboplatinum along with 5 FU.

Median survival rates for people with distant metastases range from 8 to 34 months.

Worldwide in 2002 there were an estimated 30,400 new cases of anal cancer. It is typically found in adults, average age early 60s. In the United States, an estimated 800 to 900 people die of anal cancer annually.