"For the last 15 years guidelines have suggested that women with several prior normal Pap tests can be screened less often than every year. We've demonstrated how much extra risk can be expected if such a woman elects to extend her screening interval to three years," said lead author George Sawaya, MD, associate professor of obstetrics, gynecology and reproductive sciences at the University of California, San Francisco.
The study notes that for women over age 30 who have already had a minimum of three negative, consecutive annual Pap tests, extending the screening interval from one year to three years carries a small risk, on the order of 3 or fewer cancers per 100,000 people, according to the researchers.
"As a comparison, this risk is similar in magnitude to annual breast cancer incidence in men ages 45-64 (1 to 4 per 100,000). In fact, this risk is smaller than the risk associated with everyday events such as driving, jogging, and walking, which carry estimated annual risk of death ranging from 3 to 16 per 100,000, said K. John McConnell, PhD, of Oregon Health & Science University and a co-investigator on this study.
According to Sawaya, a Pap test is the standard way physicians screen for malignant cells or cell changes that might develop into cervical cancer. Since its widespread adoption in the 1960s, health care providers have performed the Pap test primarily as part of a routine annual pelvic exam.
The major goal of screening is to identify precancerous cervical lesions, the treatment of which prevents cervical cancer. Pap test screening has been credited with profound decreases in cervical cancer in the US.
Researchers analyzed 1.2 million screening result records from the National Breast and Cervical Cancer Early Detection Program administered by the Centers for Disease Control and Prevention (CDC). Since 1991, CDC has collected Pap test results and subsequent cervical biopsy results on Program participants.
Among 31,728 women ages 30-64 years who had at least three negative consecutive Pap tests and who continued to be screened in the Program, no cases of cervical cancer were identified and only 15 women were diagnosed with precancerous lesions within the following three years.
The researchers then used a validated simulation model to predict the chance that an individual woman would develop cancer over a three-year period if she were screened annually for three years compared to once three years later. The risk associated with being screened annually was 1 to 2 per 100,000 compared to 1 to 5 per 100,000 by waiting three years. The extra risk ranged from 1 to 3 per 100,000.
Co-researcher Herschel Lawson, MD, of CDC, noted that the findings of this study further validate the decision of the National Breast and Cervical Cancer Early Detection Program to lengthen the screening interval of Program-enrolled women with multiple, consecutive normal Pap tests and concentrate resources on identifying and screening women who are rarely or never screened. These women account for over one-half of all cases of cervical cancer that occur in the US each year.
Cervical cancer is diagnosed in an estimated 12,000 women in the US each year, according to the American Cancer Society.
"Our study provides women with risk information they can use with their clinicians in making informed decisions about how often to be screened. It is important, however, for women to discuss their medical and screening history with their clinicians to determine if they are indeed good candidates for less-frequent screening," Sawaya added.
These calculations, the researchers said, will also be useful to put into context the additional benefits in terms of cervical cancer protection that newer screening methods such as liquid-based cytology and concurrent testing for cancer-causing strains of human papillomavirus may provide.
The study was funded by the CDC.
Additional authors are Shalini Kulasingam, PhD, Duke University Medical Center; Karla Kerlikowske, MD, UCSF; Joy Melnikow, MD, MPH, University of California, Davis; Nancy Lee, MD, CDC; Ginny Gildengorin, PhD, UCSF; Evan Myers, MD, MPH, Duke University Medical Center; and A. Eugene Washington, MD, UCSF.
Journal
New England Journal of Medicine