Study Finds Pap Test OK Every 3 Years

October 15, 2003
News Office: Eve Harris (415) 885-7277

Many women can safely extend their cervical cancer screening interval to three years, according to a new study published in The New England Journal of Medicine.

"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 Dr. George Sawaya, obstetrician-gynecologist at UCSF Medical Center.

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 three or fewer cancer cases 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 to 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 three to 16 per 100,000, said K. John McConnell, Ph.D., of Oregon Health and Science University and a co-investigator on this study.

According to Sawaya, a Pap test is the standard way doctors 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 United States.

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, the CDC has collected Pap test results and subsequent cervical biopsy results on Program participants.

Among 31,728 women ages 30 to 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 withprecancerous 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 one to two per 100,000 compared to one to five per 100,000 by waiting three years. The extra risk ranged from one to three per 100,000.

Co-researcher Dr. Herschel Lawson, of the 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 United States 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, also will 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, Ph.D., Duke University Medical Center; Dr. Karla Kerlikowske, UCSF; Dr. Joy Melnikow, M.P.H., University of California, Davis; Dr. Nancy Lee, CDC; Ginny Gildengorin, Ph.D., UCSF; Dr. Evan Myers, M.P.H., Duke University Medical Center; and Dr. A. Eugene Washington, UCSF.

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