In their report on cervical cancer screening released yesterday, the Centers for Disease Control and Prevention (CDC) startlingly estimated that 22 million women in the United States may have undergone such screening unnecessarily, because they had already had hysterectomies.
An expert approached by Medscape Medical News to comment on the issue cautioned that the data collected by the CDC were from women self-reporting and so may be subject to bias. She also suggested that some of the unnecessary testing, which is contrary to guidelines that have been in place for a decade, may be due to confusion stirred up by educational campaigns for the human papilloma virus vaccine Gardasil (Merck & Co).
The CDC analyzed data collected from 2000-2010 by the Behavioral Risk Factor Surveillance System on screening for cervical cancer using the Papanicolaou (Pap) test.
In one of the articles published in Morbidity and Mortality Weekly Report, the CDC highlighted the fact that during the study period, screening in women after a hysterectomy had declined from 73.3% in 2000 to 58.7% in 2010.
But this means that more than one half of the women were undergoing Pap tests unnecessarily, because hysterectomy involves removal of the cervix in the majority of cases (94% of cases, the CDC estimates).
Such women do not need cervical cancer screening - and it has been specifically discouraged in guidelines from all the major organizations since 2002-2003.
Several media reports highlighted this finding and emphasized the huge waste of financial resources this involves.
Who has screening?
If you are between the ages of 25 and 60 in the UK, the NHS cervical screening programme will contact you every 3 to 5 years and ask you to go for a cervical screening test. The exact age groups for screening vary between the different countries of the United Kingdom.
In England and Northern Ireland, women between 25 and 64 years are screened.
In Scotland, women between 20 and 60 are invited for screening.
In Wales, women between 20 and 64 are screened.
Why the screening interval varies
The screening interval is the time between the screening tests. This used to vary between health authorities. But research reported in 2003 by Cancer Research UK showed that the screening interval should be decided by age. We can pick up the most cancers by screening women every 3 years if they are 25 to 49 years old and every 5 years if they are between 50 and 64.
For women between 25 and 49, 3 yearly screening prevents 84 cervical cancers out of every 100 that would develop without screening. 5 yearly screening will only prevent 73 cancers out of 100. So the guidelines now recommend screening women 3 yearly if they are under 50.
It is acceptable and safe for women of 50 or more to have 5 yearly smears. Screening 3 yearly doesn’t give any extra protection for this age group. This is probably because abnormal cells develop more slowly in women over 49.
The NHS in England and Northern Ireland have adopted these recommendations. So if you are between 25 and 49 and live in England or Northern Ireland, your health authority will offer you 3 yearly cervical screening.
The CDC itself commented that in this population, any benefit from screening “might be outweighed by the net harm.” Such harm may include false-positive tests leading to needless patient anxiety and invasive procedures.
“The false-positive rate…is indeed a great potential harm to women and cost to the healthcare system,” says Diane Harper, MD, MPH, professor of community and family medicine/obstetrics and gynecology at Dartmouth Medical School, in Hanover, New Hampshire, and director of the Gynecologic Cancer Prevention Research Group at the Norris Cotton Cancer Center.
Medscape Medical News approached Dr. Harper to shed some light on some of the findings from the survey.
Self-Report Data Are Subject to Bias
Dr. Harper emphasized that the data are based on self-reporting, and thus are subject to bias.
“We have ample evidence to show that women of all ages are not cognizant of what a Pap test is,” Dr. Harper said. “Most women believe that anytime they have an examination of the pelvic area, whether a speculum was used or not, they had a Pap test.”
This has been shown in multiple research studies, and it raises questions concerning the validity of the self-report nature of the CDC survey, she said. “Hence, what is really being compared is whether women’s perceptions of having had a Pap test have changed with the new guidelines.”
“The second issue with the CDC survey data,” she continued, “is that the answers women can choose for frequency of Pap testing are hard for women to internalize. Most women can distinguish ‘never’ from ‘ever. ’ And most women can distinguish within the past 12 months/year. But at frequencies longer than a year, there is very poor recall accuracy, leading to tremendous bias how the data are interpreted.”