Information for general practitioners
Anal cancer is rare in the population, but should be considered in those whose demography, behaviours or immunological status may increase risk.
Most patients with anal cancer give a history of increasing anal lumps or fresh rectal bleeding.
After taking a history, the most important examination is visual inspection and a Digital Anal Rectal Examination (D.A.R.E.). Any anal swabs should be taken before the DARE, as lubricant may interfere with testing technologies.
What is an anal swab test?
The anal Pap test is a method for screening for anal cancer and precancerous lesions. It essentially uses the same techniques as those of cervical screening.
Note that this technique is still being evaluated, and that there is currently no Medicare rebate.
How can I take an anal swab test?
It is very important that you appropriately counsel your patients regarding the potential risks and benefits of the procedure before undertaking an anal swab smear.
It is currently unknown whether anal douching prior to taking the test affects the quality of the specimen.
Material from the lining of the anal canal are collected using a Dacron swab, pre-moistened with tap water. It is inserted 5cm, directly into the anal canal, without the use of a proctoscope. In a spiral manner, and with firm pressure, it is rotated and gradually withdrawn over a 1 minute period.
The swab is then eluted into a fixative (such as ThinPrepTM) and sent to a laboratory. The specimen can be tested for the presence of high risk HPV genotypes.
Consider screening for other anal STIs, if the history suggests that the person may be at risk.
Cytological examination of anal specimens is quite specialised, and you should first discuss this with your local laboratory before sending any material.
What are the potential problems?
The procedure itself is usually well tolerated, although some people have some mild discomfort during and immediately after the swab has been taken. Rarely, minor bleeding is noted for a short while afterwards.
What will the anal swab test result be?
The result will be one of:
- Technically inadequate – this is usually because inhibitors are present in the specimen or the internal controls fail to identify human cells
- Negative – no high risk HPV genotypes identified. This is usually because no infection is present. However, on occasion, high risk HPV infection is present, but at very low levels. If there is a high index of suspicion, consider repeating after a few weeks.
- HPV 16 detected – this is the most common HPV genotype found in anal cancers. However, most people with HPV16 do not develop anal cancer. It is used in some screening programs to refer patients for further investigation by High Resolution Anoscopy.
- Other high risk HPV detected (including HPV 18). These genotypes are less commonly found in anal cancers, but are more common in people living with HIV. Most people with these genotypes do not develop anal cancer. Some screening programs suggest repeating the test after a few months, or testing the specimen for cytological abnormalities (like in the cervical screening program). Depending on the results, referral for HRA may be indicated.
- It is very important that you appropriately counsel your patients regarding the possible meaning of the results.
Caution is required in the interpreting of anal swab results. It is important to note that this test does not reliably detect cancer - if you have any concerns, (especially if the patient is symptomatic) then please refer urgently for a specialist opinion.
If you suspect that your patient is at very high risk of anal cancer, they may be referred to the Dysplasia and Anal Cancer Services (DACS), IBAC, Level 4 Xavier Building, at St. Vincent's Hospital, Sydney. Your patient will need a referral letter. However, if the matter is urgent, please ring (02) 8382 3707.