HPV (Human Papillomavirus)
HPV is the most common sexually transmitted infection (STI) and almost all sexually active adults will have HPV at some point in their lifetime. HPV is contracted through skin-to-skin contact.
- There are over 200 strains of HPV; 40 strains are sexually transmitted.
Sexually transmitted HPV can be classified as either low-risk or high-risk. Low-risk HPV can be responsible for genital and anal warts. Two high-risk strains of HPV that are responsible for the majority of HPV-related cancers are HPV-16 and HPV-18. At least 90% of all anal cancers are caused by HPV - the vast majority by HPV 16.
- For most, the immune system will clear the body of an HPV infection within 2 years. For others, HPV may persist or lay dormant for years and, occasionally, may result in either precancerous lesions or cancer.
- HPV is responsible for 5% of cancers worldwide, including: anal cancer, cervical cancer, oropharyngeal cancer, penile cancer, vaginal cancer and vulvar cancer.
- Currently there are two vaccines that protect against HPV, Gardasil and Cervarix. Gardasil protects against HPV 6, 11, 16 and 18. Cervarix protects against HPV 16 and 18. In many countries, both vaccines have been approved for the use in girls and women. More countries are approving the vaccine for use in boys and men each year.
AIN (Anal Intraepithelial Neoplasia)
When the human papillomavirus infects healthy tissue, it can slowly change the cells to become abnormal. These abnormal cells are classified in three stages: LSIL (AIN 1) and HSIL (AIN 2 or 3). The more abnormal the cell becomes, the higher the stage; AIN 1 is the least severe and AIN 3 is the most severe of the three.
- AIN 1 is also known as low-grade dysplasia. It can have appearances that are similar to warts.
- AIN 2/3 are also known as high-grade dysplasia or high grade squamous intraepithelial lesions (HSIL).
- Some cases of AIN 2/3 may progress to anal cancer over time.
- There is no standard for how to treat AIN. Some cases will regress, if left untreated, however it is difficult to predict which ones will do this. The HOST study will examine effective screening and treatment protocols for high-grade anal intraepithelial neoplasia.
- High-grade lesions (HSIL or AIN 2/3) are more common in those who are HIV+.
Anal cancer is a rare form of cancer that occurs in the cells and tissue of the anus. Anal cancer includes HPV infection as a precursor to the disease. Anal cancer rates are increasing in all countries where it has been studied.
- Most cases have no symptoms in the early stages.
- When they do occur, symptoms may include: abnormal bowel habits, anal bleeding, anal itching, a lump near or in the anus, anal pain or pressure, or mucous from the anus. However, these symptoms can be caused by many other conditions so it is important to have them carefully checked out.
- Screening methods include: digital ano-rectal examination (DARE) --in which a clinician inserts a gloved finger into a patient’s anus to detect any abnormalities, anal Pap smear- when the anus is swabbed to detect abnormal cells that may be precursors to anal cancer, and high resolution anoscopy (HRA) - when a microscope is used to determine where anal tissue changes are located, and to guide biopsies.
- Anal cancer is diagnosed on biopsy, where specimens are carefully looked at in the laboratory.
- Staging is the process where the extent of spread of the cancer is determined. It uses scans such as MRI and PET. Depending on staging, treatment options will vary. For very early stage localized cancers, excision by surgery may be an option. However, most cancers are treated with a combination of chemotherapy and radiotherapy. Occasionally a colostomy is needed.
- There are many types of anal cancer: squamous cell carcinoma (most common), cloacogenic carcinoma, adenocarcinoma, basal cell carcinoma, and malignant melanoma.
- In 2014, it is estimated that 7,210 people will be diagnosed with anal cancer in the US. Of these cases, about 62% will be women and 38% will be men. However, the highest rates are in HIV-infected gay men. Others who are immunosuppressed (such as those with transplants) are also at higher risk.