Posted 11/2/11 on The Doctor Weighs In
There are an increasing number of do-it-yourself (DIY) technologies that allow individuals to test for different diseases (e.g., HIV) or monitor chronic conditions (e.g., diabetes, hyperlipidemia). Now home testing for human papillomavirus (HPV) has been added to the mix. The reason why this is important is that a recent large randomized trial has shown that home-based sampling for HPV is three times as sensitive as conventional Pap smears in detecting advanced HPV-related lesions or cancer. For invasive cancer, the home HPV sampling was more than four times as sensitive as cytology.
In a study, led by Attila Lorincz PhD of Queen Mary University of London, more than 20,000 women in poor areas of Mexico were randomly assigned to either home-based vaginal HPV sampling or to traditional clinic-based Pap smear testing. Close to 10% of the 9,202 women tested by the home-based HPV method were found to be positive for the virus. All were referred for colposcopy (direct visualization of the cervix). Approximately, half of the group that had colposcopy had suspicious lesions that were then biopsied. Of the 432 biopsies, 137 had cervical intraepithelial neoplasia (CIN) 1 (mild dysplasia), 60 had CIN 2 (moderate dysplasia) and 20 had CIN 3 (severe dysplasia, sometimes referred to as carcinoma in situ). Only 28 out of the 9,202 women screened had a diagnosis of cervical cancer.
Cervical intraepithelial neoplasia (CIN) is a potentially premalignant transformation and abnormal growth of squamous cells on the surface of the cervix. Some of these lesions, particularly CIN 1, can regress as a result of the body’s own immune response; however other CIN lesions, such as CIN 2 or 3 can progress to full-blown cervical cancer.
So the good news is that home HPV testing is sensitive – in fact, the study found it was 3.4 times as sensitive as Pap smears at picking up CIN 2 or worse lesions. It was even more sensitive at picking up invasive cancers. That means more women with those lesions will be correctly diagnosed and, hopefully, referred for definitive treatment.
The bad news is that the postive predictive value – the percent of people testing positive who actually have the disease – is much worse for home testing compared to clinic-based Pap smears (12.2% versus 90.5%). What that means practically is that, as was shown in this study, you will refer a lot of women for advanced testing with colposcopy who won’t turn out to have the disease.
For those who think “better safe than sorry” when it comes to screening, there are lessons to be learned from the world of prostate cancer screening or even “whole body CT screening.” Both of these ended up subjecting people with positive findings to further testing, sometimes invasive, only to show that the positive screening test was actually a false positive (screened positive, but did not have the disease). There are costs, both economic and human suffering, associated with any kind of screening test. A careful study of the benefits and risks must be done to determine exactly how these tests should be used in practice. Further, we need to understand if we can improve benefit/risk ratio by modifying the test (HPV subtyping) or refining the testing strategy (e.g., factoring in co-morbid conditions, other biomarkers, etc.).
That being said, the addition of home HPV testing to the cervical cancer screening armamentarium is a valuable addition. It means women who may not have been screened before because of lack of access to traditional screening methods will now be tested. As technology increasingly allows us to move health care from the clinic and hospital into the home, I believe we will all benefit.
Patricia Salber MD, MBA is a former Internal Medicine Emergency Physician and large health plan Chief Medical Officer. She writes at The Doctor Weighs In.