Pap test every year? Not for every woman
New recommendations say a Pap test every 3 years is sufficient in some women. Solid data explain why, but old habits are hard to change.
Frequent screening until age 30 allows us to identify and treat young women with histologic cervical intraepithelial neoplasia (CIN) 2 and 3 or worse, and to identify those who, because of persistently negative Pap tests, are at lowest risk.
Since these women schedule more frequent visits for contraception and prenatal care, we have greater opportunities for cervical cancer screening.
Does type of Pap test determine screening interval?
Every 2 years is sufficient if the liquid Pap test is used: ACS.1 This recommendation is based on balancing the increase in abnormal results found with liquid-based Paps against the likelihood that most of the additional abnormal findings will be only atypical squamous cells, undetermined significance (ASC-US) or low-grade squamous intraepithelial lesions (LSIL). These minimally abnormal results, while needing follow-up, have a relatively low rate of CIN 2 or 3 on biopsy.
Annual tests until age 30, irrespective of Pap technology: ACOG.2 That decision recognizes the fact that, while the data suggest increased sensitivity of liquid-based cervical cytology, this observation is not conclusive, and both technologies fall short of 100% sensitivity.
AGES 30 TO 65Why extend the interval between Pap tests?
High risk calls for yearly screens
Both ACOG and the ACS agree that women at high-risk should be screened annually regardless of age.
Risk factors include:
- history of cervical cancer,
- immunocompromise including HIV,
- in utero exposure to diethylstilbestrol (DES), and
- women over age 30 who were not well screened in their 20s; these women should have at least 3 negative annual exams before the screening interval is extended.
Longer interval if risk is low
Up to age 30, frequent screening can be expected to significantly reduce a woman’s risk of cervical cancer. Multiple negative Paps offer a high degree of protection—the more consecutive normal tests, the higher the level of protection.13
Research indicates, however, that it seems reasonable to reduce the screening interval from every year to every 2 to 3 years in previously well-screened women over age 30:
- These women have the protection offered by frequent Pap tests during the previous decade.
- By the time most women reach their 30s, the area of active squamous metaplasia, which serves as the substrate for cervical neoplasia, is reduced.14
Studies of screening effects
National Breast and Cervical Cancer Early Detection Program. Using data from this program, Sawaya et al13 studied 31,728 women aged 30 to 64 with 3 or more consecutive negative Pap tests spaced no more than 3 years apart. They found only 9 women (0.028%) with biopsy-proven CIN 2, only 6 (0.019%) with CIN 3, and none with invasive cancer.
International Agency for Research in Cancer15 data showed essentially no difference in the protective effect of cytology screening at 1-, 2-, or 3-year intervals in women enrolled in screening programs in 7 Western European countries and 3 Canadian centers, among women aged 35 to 64 who had at least 2 previous negative Pap tests. The authors calculated a cumulative reduction in cervical cancer of 93.5% with annual screening, 92.5% with screening every 2 years, and 90.8% with screening every 3 years, compared to women who had no screening.
National Breast and Cervical Cancer Early Detection Program16 data also support extending the screening interval beyond 1 year. In 128,805 women followed after at least 1 prior negative Pap, no significant difference was noted in the incidence of cytologic HSIL on a subsequent Pap performed 9 to 12 months, 13 to 24 months, or 25 to 36 months later. The rates of HSIL were 25, 29, and 33 per 100,000 women, respectively.
Do postmenopausal women need screening?
Women over 65 do get cervical cancer. While they represent 13% of the total U.S. population, they have 25% of new cases of cervical cancer and suffer 41% cervical cancer mortality.17 Incident cases of squamous cancer among older women, however, come from the cohort who have not previously been well screened.
An older woman in a long-term monogamous relationship who has a history of frequent negative Pap tests is at such low risk for acquiring cervical cancer that the US Preventive Services Task Force recommends discontinuing screening in this group at age 65.3
The American Cancer Society recommends discontinuing screening at age 70 in low-risk previously well screened women.1
ACOG does not set a specific upper age for cytology screening.2 While acknowledging the recommendations of these other professional organizations, ACOG notes that there is no good evidence to establish one age over another to discontinue screening, and instead encourages individualization.
ACOG recommends that if an older woman’s sexual practice changes after she is no longer being tested with cytology, some consideration should be given to reinitiating screening. If screening is restarted, 3-year intervals seems appropriate, as older women may have immunity to many HPV types, and their active transformation zone is generally retracted and very narrow.
