Declines in cervical cancer incidence and mortality reported in the United
States since the 1950s have been attributed to early detection and treatment of
precancerous and cancerous lesions through the use of the Papanicolaou (Pap) test
(1). More than 50 million Pap tests are performed each year
(2); however, guidelines about the
frequency of testing in women with a history of normal test results are inconsistent
(3--5). To determine the incidence of cervical cytologic abnormalities following a normal Pap test,
1991--1998 data from the National Breast and Cervical Cancer Early Detection
Program (NBCCEDP) were analyzed for this report
(6). The findings indicated that within 3 years
of a normal Pap test result, severe cytologic abnormalities were uncommon, and
incidence rates were similar among women screened 1, 2, and 3 years following a normal Pap test.
For each woman, CDC received a report that included demographic
characteristics, Pap test results, diagnostic procedures, and histopathologic results
(6,7). To be eligible for the analysis, women were required to have had a first NBCCEDP Pap test reported
as normal during 1991--1998, and at least one subsequent Pap test performed within
the following 9--36 months. Of 620,063 women tested during 1991--1998, 128,805
(20.8%) met the criteria for eligibility. Results of Pap tests were reported using Bethesda
System categories: normal; infection, inflammation, or reactive changes; atypical squamous
cells of undetermined significance (ASCUS); low-grade squamous intraepithelial lesion
(LSIL); high-grade squamous intraepithelial lesion (HSIL); "suggestive of squamous cell
carcinoma"; and "other" (e.g., glandular atypia and atypical endocervical glands).
Incidence rates of Pap test interpretations were calculated by dividing the number
of women with each test result by the number of women retested within each age
group (<30, 30--49, 50--64, and >65 years) and time interval (9--12, 13--24, and 25--36
months). Incidence rates were age-adjusted using the age distribution of the 1996
NBCCEDP population. Ordinary least-squared regression was used to evaluate the trend of
increasing time between the first Pap test on the age-adjusted incidence of ASCUS,
LSIL, HSIL, and suggestive of squamous cell carcinoma.
The average age of women included in the analysis was 48.9 years (range:
12--96 years); 73,631 (57.0%) were non-Hispanic whites, 22,672 (17.6%) were Hispanics,
17,314 (13.4%) were non-Hispanic blacks, 10,983 (8.5%) were American Indians/Alaska
natives, 3070 (2.4%) were Asians/Pacific Islanders, and 1135 (0.9%) were categorized
as "other" or "unknown." The mean time between the first and second test was
months. Approximately 121,576 (94.4%) of the 128,805 second test results were
interpreted as normal or infection, inflammation, or reactive changes. The incidence rate
of the second test results interpreted as HSIL and suggestive of squamous cell
carcinomas was 66 per 10,000 women aged <30 years, 22 per 10,000 women aged 30--49 years,
15 per 10,000 women aged 50--64, and 10 per 10,000 women aged
>65 years (trend test, p<0.001). Overall, as age increased, the incidence of ASCUS and LSIL also
decreased (trend test, p<0.001, each category).
The age-adjusted incidence of results interpreted as LSIL increased over time
(trend test, p=0.01). The incidence of ASCUS, the most common cytologic
abnormality, did not change significantly over time (p=0.36). The differences in the age-adjusted
incidence of HSIL and suggestive of squamous cell carcinoma for the time intervals
also were not significant (p=0.42).
Reported by: GF Sawaya, MD, K Kerlikowske, MD, G Gildengorin, PhD, AE Washington,
MD, Univ of California, San Francisco. Div of Cancer Prevention and Control, National Center
for Chronic Disease Prevention and Health Promotion; CDC.
The U.S. Preventive Services Task Force recommends Pap test
screening at least every 3 years until age 65 years
(5). The American Cancer Society guidelines suggest that screening less frequent than annually may be adequate for Pap testing
in women with a history of 3 negative annual Pap tests
(3), and the American College of Obstetricians and Gynecologists recommends annual Pap tests for most women
The difference in screening annually, biennually, or triennially is substantial in
the number of tests performed and in the public health implications. In this analysis,
women screened 1, 2, and 3 years after a normal Pap test had similar risk for developing
HSIL and suggestive of squamous cell carcinoma. Other studies have indicated clinically
insignificant additional protection in testing yearly compared with triennially
(8). However, low-grade abnormal Pap results (e.g., ASCUS and LSIL) constituted >95% of the
cytologic abnormalities after the first normal results. The clinical significance of these
abnormalities is unclear. Women who were screened annually rather than less
frequently might have worse health outcomes if low-grade results of undetermined clinical
importance lead to further testing and unnecessary patient morbidity and anxiety
The findings in this report are subject to at least four limitations. First, the
database used was intended for descriptive statistics and not for hypothesis testing; data
were limited to a few variables. Second, NBCCEDP serves low-income and uninsured women;
results may not be generalizable to other groups. However, low-income and
uninsured women usually are at greater risk for developing cervical neoplasia than women
with higher incomes; therefore, higher-income women should be less likely to exhibit
higher rates during the 3-year interval examined in this study. Third, women may have
received Pap testing outside the program during the time between the first and subsequent
Pap tests; however, this probably occurred in only a few women. Finally, women who
frequently get screened, specifically within 1 year after Pap test, might be low-risk
women concerned about their health or high-risk women with histories of abnormal Pap
tests who have been told to get annual tests. Other risks for cervical cancer in these
women and whether these risks affected the findings in this study are unknown. NBCCEDP
receives data from many cytopathology laboratories and clinical settings. The findings
in this study may better represent actual clinical settings than the findings in a
CDC is working with state health departments to use this information as a basis
for cost-effective strategies to reach women who have not received screening services
for cervical disease. CDC will assist NBCCEDP in assessing program-provider
practices, modifying patient recall systems, and developing professional and public education
strategies to improve patient-provider decision making. Further research is needed to
clarify the benefit and harm related to frequency of subsequent Pap testing in women
with normal results.
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