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Clinical Reviews


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.

December 2004 · Vol. 16, No. 12

COMMENTARY

Putting new guidelines into practice is easier said than done

Steven Goldstein, MD
New York University Medical Center

Is the Pap test still necessary for every woman, every year? No, according to the latest guidelines, but old habits die hard, even for physicians.

And there is little doubt that yearly screening, though not scientifically based, has contributed much to the reduction of cervical cancer incidence and mortality in American women. Our patients and we as providers have long considered a Pap test the cornerstone of the annual gynecologic exam, as we’ve been urged to do for decades by our leading academic institutions. However, the American College of Obstetricians and Gynecologists (ACOG) and the American Cancer Society (ACS) revised their guidelines last year, and no longer support yearly screening for every woman, every year.1,2 The US Preventive Services Task Force (USPSTF) revised its guidelines in accord, with the exception that it found the evidence insufficient to support screening low-risk women more often than every 3 years, at any age.3

Original rationale: “Pap smear prompt”

These organizations, as well as the National Cancer Institutes (NCI), had supported annual Pap testing since the mid-1950s—long before any data suggested whether one screening interval might be better than another.

In fact, part of the original rationale for annual screening was that it would serve as a vehicle to bring women in for their annual gynecologic exam.4

INTEGRATING EVIDENCE AND EXPERIENCE

Frequent screening would detect exceedingly few additional cancers, at an exceedingly high cost

We can confidently counsel patients

A previously well-screened woman over age 30 who has no history of dysplasia has an exceedingly small risk of cervical cancer, whether her next Pap test is 1, 2, or 3 years after her last.

How many cancers will we miss?

Miller MG, Sung HY, Sawaya GF, Kearney KA, Kinney W, Hiatt RA. Screening interval and risk of invasive squamous cell cervical cancer. Obstet Gynecol. 2003;101:29-37.

This matched case-control study assessed the odds of being diagnosed with squamous cell cervical cancer when a Pap test is performed 2 or 3 years versus 1 year after a normal Pap. Data from the Kaiser Permanente Medical Care Program in Northern California was used to identify 482 women who were diagnosed with invasive squamous cell cervical cancer between 1983 and 1995, and to compare each woman with 2 control individuals matched for age, race/ethnicity, and length of program membership. An intact cervix and no prior cervical, uterine, or vaginal cancer were required. A woman who had a Pap test within 18 months of her last negative test was half as likely to have invasive cancer as a woman who waited 3 years (31 to 42 months).

The odds ratios for invasive cancer diagnosed by screening at 1, 2, or 3 years were 1.00, 1.72, and 2.06, respectively. The differences between intervals of 2 or 3 years versus 1 year were significant. The odds ratios increased to 2.15 and 3.60, respectively, in women with at least 2 consecutive negative Pap tests prior to diagnosis.

In all analyses, the odds ratios continued to increase as screening intervals were prolonged beyond 3 years.

Increased relative risk and very small absolute risk. The new ACOG and ACS guidelines recommend extending the screening interval only for women over 30 who have been well screened over the previous decade. This study does not break down the relative risks by age, nor does the sample size allow assessment of the risks for women with more than 2 consecutive negative Paps.

The authors note that the age-adjusted incidence of invasive cervical cancer among all Northern California Kaiser Permanente members is only 6.2 per 100,000 women. In this well-screened population, even doubling the relative risk leaves a very small absolute risk of cervical cancer.

How many fruitless interventions?

Sawaya GF, McConnell KJ, Kulasingam SL, et al. Risk of cervical cancer associated with extending the interval between cervical-cancer screenings. N Engl J Med. 2003;349:1501-1509.

If screening were done annually rather than every 3 years, how many additional tests would be needed to diagnose each additional cancer expected to be found? To find out, Sawaya et al applied data from the National Breast and Cervical Cancer Early Detection Program to a Markov model. They studied 32,230 women with 3 successive negative Pap tests, each no more than 36 months apart.

They predicted that, in a theoretical cohort of 100,000 women who had at least 3 consecutive negative Pap tests, screening at 1-year rather than 3-year intervals would uncover 3 additional cancers in women aged 30 to 44, a single additional cancer in women aged 45 to 59, and no additional cancers for women 60 to 64 years of age.

They calculated that, for this theoretical cohort of 100,000 women:

  • To find all 3 additional cancers in the 30- to 44-year-old group would require 69,665 Pap tests and 3,861 colposcopies.
  • To find the only additional cancer in the 45- to 59-year-old group would require 209,324 Pap tests and 11,502 colposcopies.

As with all modeling studies, Sawaya’s analysis is limited by the assumptions introduced into the model.

Among them:

  • perfect compliance on the part of this cohort of hypothetical patients,
  • use of conventional Pap tests only, and
  • uniform sensitivity and specificity.

Why change? How will patients react?

Cumulative findings suggest an age- and risk-based approach

Research over the past few decades has revealed much about the pathogenesis of cervical cancer which supports an age- and risk-based approach to screening for cervical cancer—when to start, when to stop, and how often to perform cervical cytology.

The main questions

In this article, I’ll review some of the data on these concerns:

  • Why wait 3 years after first intercourse for the first Pap test?
  • Why is 21 the ‘default’ age for first Pap test?
  • What are the risks and costs of screening every 2 to 3 years in well-screened women over age 30? Over age 65?
  • Do most women without a cervix require screening?
  • What is the role of HPV DNA testing?
  • How should we deal with abnormal results?
  • How should we counsel the patient?
  • What’s the harm in continuing Pap tests in all women?
  • Will women return for annual exams as we advise, if we change their Pap test routine?

ADOLESCENCEWhy wait 3 years after onset of intercourse for first Pap test?

Care is not compromised

Delaying screening until at least 3 years after coitarche does not compromise the diagnosis of high-grade lesions, yet does allow discovery and eradication long before they become malignant. On the other hand, screening young women sooner than 3 years after first sexual intercourse risks diagnosing numerous self-limited HPV infections and transient low-grade dysplastic lesions, which have very low premalignant potential.

Persistent high-risk HPV must precede cancer. Cervical cancer develops only after persistent HPV infection, many years from the initial HPV exposure.

We now know that at least 15 to 18 types of human papillomavirus (HPV) can cause cervical cancer, and that infection with a high-risk type of HPV is the necessary antecedent—but not by itself a sufficient antecedent—for high-grade cervical dysplasia and cervical cancer.5,6

We also know that HPV is most often acquired through sexual intercourse and that it is very efficiently acquired by young women.7,8 For example, a study of young college women who were initially HPV negative acquired HPV at a rate of 14% per year.7

HPV infections in young women are usually transient, however. Up to 90% of young women who test positive for HPV DNA will revert to negative within 2 years.9

The problems of screening too early. Squamous cancer of the cervix is exceedingly rare in women under age 21.10 Diagnosis of self-limited HPV infections and transient low-grade dysplastic lesions would likely result in repeat Pap tests and colposcopies. In addition to being costly and anxiety-provoking, these interventions may lead to needless destruction of the immature transformation zone in young women of low parity.

Don’t neglect counseling, STD testing, birth control

Delaying the first Pap test in young women until 3 years after initial intercourse, however, does not mean we should neglect gynecologic examinations in this group. They are at high risk for sexually transmitted infections and at extremely high risk for unintended pregnancies. So, while waiting 3 years to do the first Pap test makes sense, an early visit, before or soon after first intercourse is essential for gynecologic health care, including prevention of pregnancy and sexually transmitted disease.

October 2004 opinion on Gyn visits for young teens. ACOG published a committee opinion11 to clear up confusion over when adolescent girls should have their first Pap test versus when they should have their first gynecologic visit. The opinion advises a first visit at age 13 to 15, for health guidance, screening, and preventive services, and says parents and patients need to understand that this visit does not necessarily include a pelvic exam or a Pap test. The advisory stresses that adolescents are unlikely to acknowledge sexual activity without sensitive and direct questions, and suggested a resource: “Asking the Right Questions,” from the STD/HTD Prevention Training Center of New England.

AGES 21 TO 30Why is age 21 the “default” for first Pap?

Because the incidence of high-grade squamous intraepithelial lesions (HSIL) increases with age,12 cytology screening should start at age 21, irrespective of sexual history. Saslow et al1 writing for the American Cancer Society, acknowledged the difficulty of obtaining a reliable sexual history. This may be especially true with patients who may have suffered sexual abuse as adolescents. The default age of 21 for initial Pap test allows the provider to sidestep the question of age at first intercourse. On the other hand, a 21-year-old who has never had vaginal intercourse does not need to be screened for cervical cancer.

Aggressive screening until age 30

Women should be screened every year until age 30 if conventional Pap smears are used.1,2 During a woman’s 20s, precancerous lesions become more common and invasive cancer, while still rare, is seen with increasing frequency. Both ACOG and ACS consider this period of a woman’s life to be a time for aggressive cervical cancer screening.

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

Continued...
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