Ever since the American Cancer Society’s announcement last week that breast and prostate screening tests may not be all that they are cracked up to be, women have been more confused than ever about the benefits of common tests for early cancer detection. Many experts spoke out emphasizing the importance of early detection of cancer through screening tests and the Pap test to detect cervical cancer early was once again described as the gold standard.
To confuse things further, a new study published in JAMA of nearly 90,000 women finds that a commonly used alternative to conventional Pap tests, called liquid-based cytology, is not any better at detecting pre-cancerous growths than the standard dry or slide method. However, regardless of which method your doctor uses for the Pap test, the Pap test is still not perfect. The Pap test needs to be partnered with the most up to date science and practice, including the HPV test. So how to make sense of the Pap test? What should women ask for? What about this newer HPV test? Who should get what test and why?
First let me give you some background on the Pap test and cervical cancer. Until the Pap test was widely adopted in the United States in the late 1940’s, cervical cancer was the number one cause of cancer death in women. After the widespread use of the Pap test however, cervical cancer cases dropped by 70%. This is a huge success story. (By the way, it remains the number two cause of death worldwide and in very poor countries it tops the list of deadly cancers because many countries cannot afford the costs associated with Pap tests.)
By 1999 the World Health Organization concluded that there was a single cause of cervical cancer – the Human Papilloma Virus (HPV). HPV is a simple double-strand of DNA enclosed in a protein capsule that resembles a soccer ball when viewed under a special microscope. Although there are over 100 types of HPV, only about fifteen types are linked to cancer. These fifteen types are commonly called “high risk strains” of the virus.
Soon after the discovery of HPV as the cause of cervical cancer, a DNA test to look for the high risk strains of HPV was developed. This simple test is done using the same scraping of cells used for the Pap test. Research in the past few years published in the Lancet and the New England Journal of Medicine suggests that screening with the HPV test rather than the Pap test may lead to more women diagnosed with abnormal precancerous cell changes and potentially save more lives, especially in countries where regular Pap testing is not an economic alternative.
The Pap test looks for cell changes under the microscope caused by the virus and is not foolproof. On occasion the cell changes are not discovered and cervical cancer is eventually discovered. One of my sisters was diagnosed with cervical cancer earlier this year despite previously normal Pap tests.
On the other hand, there are other causes of a mildly abnormal Pap test besides HPV, such as low estrogen in women after menopause. I had an abnormal Pap test after menopause which was from low estrogen and not from HPV.
The HPV test checks for the presence of the virus itself and will be positive even if cell changes aren’t yet evident. Although most women are exposed to HPV at some point in their lives (which is why we suggest that all women undergo cervical cancer screening), most women will fight off the virus within a year or two and the virus either disappears altogether or remains dormant. Only about five per cent of women will not fight off the virus and these women will continue to test positive with the HPV test. It is only this small group of women who are at risk for eventually developing severe cell changes and cancer if these cell changes aren’t treated.
So now back to the recent JAMA study suggesting that both the dry slide type Pap test is as good as the more expensive liquid-based Pap tests. As it turns out, most labs in the US are already using the liquid-based Pap test. Because the newer HPV test must be done on cells placed in liquid, continuing to use the liquid Pap method makes the most sense for women who may also need the HPV test if their Pap test is abnormal or “inconclusive” or if they are 30 years of age or over and want to be screened with both tests at the same time.
The American Cancer Society remains firmly committed to their message that all women should be screened for cervical cancer. They should be applauded in their efforts to eliminate cervical cancer. It was the American Cancer Society that worked tirelessly over the years to alert women to the need for a regular Pap test and I hope this strong message doesn’t get lost on young girls and women.
Here is a quick review of the recommendations that make the most sense to me:
1) All young girls and women should begin an annual Pap test starting 3 years after they became sexually active or by age 21. It takes about 3 years from the time a woman is exposed to HPV to develop serious cell changes that can be detected with the Pap test.
2) Any inconclusive or mildly abnormal Pap test result should lead automatically to the HPV test. Women who have a mildly abnormal Pap test and also test positive for high risk HPV need more testing such as a colposcopy and closer follow up. Women who don’t have high risk strains of the virus can simply have their Pap test repeated in 6-12 months.
3) Starting at age 30, women should ask to have an HPV test at the same time as their Pap test. If they have a normal Pap test and no high risk strains of HPV, they can safely have a repeat check for cervical cancer every 3 years. That doesn’t get women off the hook for the all important regular check up including a pelvic exam however.
4) Women who have had a hysterectomy and their cervix removed for benign conditions such as fibroids or heavy bleeding can stop having Pap tests altogether.
5) Women who have had a hysterectomy for cancer should continue with regular Pap and HPV testing. The vulvar, vaginal and rarely anal tissues can also develop precancerous cell changes and even cancer from high risk strains of HPV.
6) Women who remain sexually active long into their adult lives should continue to be checked regularly for cervical cancer. As always, I welcome your thoughts and suggestions.
Marie Savard, M.D.
ABC News Medical Contributor
Author of Ask Dr. Marie: Straight Talk and Reassuring Answers to You Most Private Questions
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