Should I have a Pap smear every year?

By Abigail Mellier, | Health | 0 Comments

Annual Pap smears are an important part of regular health exams for women during their childbearing years. Microscopic examination of cells scraped from the cervix allow the early detection of changes that indicate cancer of the cervix of the uterus, or sometimes cancer of the uterine lining (the endometrium). After the menopause, cancer of the cervix becomes less common, and some physicians wonder if an annual Pap smear is still necessary. A study at University of California, San Francisco has examined this question.

Pap smears were collected annually from postmenopausal women taking part in a large study of the effects of a combination of hormones - the Heart and Estrogen/progestin Replacement Study (HERS). There were over 2,500 women in the study, with half given the hormone combination and half a placebo, for just over 4 years. Their average age was 67.

Strict definitions were set up for classifying smears as normal or abnormal. Attention was focused on the women who had a normal Pap smear at baseline, and then had an abnormal one at the one year or two year exam.

After one year, 78 women (3%) of those who had a normal smear at baseline were found to have an abnormal smear. After the second year, an additional 32 women (1.4%) had an abnormal smear. This means that 2.25% of postmenopausal women are likely to develop an abnormal Pap smear in the two years after a normal smear. But what does this actually mean?

All 110 women in the study who developed an abnormal smear in the first 2 years were followed up carefully. In addition to the results of examinations made during the remaining 2 years of the study, questionnaires were completed with information about known risk factors for cancer of the cervix - e.g. cigarette smoking, number of children, age at first intercourse, and sexually transmitted disease. Additional procedures were carried out on the 110 women; these were: repeat Pap smears (112 instances), tissue sampling of the cervix or endometrium (96 instances), and direct inspection of the cervix using magnification (colposcopy - 33 instances). Some of these procedures called for a general anesthetic.

The follow-up information allowed a final diagnosis to be made for all but 7 of the 110 women. None of the 78 women found to have an abnormal Pap smear at one year were abnormal on final diagnosis, and only one of the 110 women with abnormal smears at one or two years had a ‘problem’ involving the cervix - a microscopic change in the surface layer of cells suggesting early cancer. (Two women were lost to follow-up, and two had findings of minor vaginal or endometrial changes; the others who hadn’t got final diagnoses had at least one normal Pap smear before the 4 years was up.)

An abnormal Pap smear followed by a normal one, or by normal gynecological findings, is called a ‘false-positive’. In this study, all but one of the ‘abnormal’ smears at the one and two year exams were found to be ‘false-positives’. However, they led to over 230 interventions (repeat smears, or diagnostic procedures sometimes involving anesthesia).

The authors of the study conclude that postmenopausal women who have had a normal Pap smear done recently don’t need a repeat smear for at least 2 years. (Obviously, this doesn’t apply to women who have never had a Pap smear, or only one several years ago.) If someone requests a Pap smear within the 2-year period, they should realize that they are more likely to have a false-positive smear, with all the investigation that entails, than to have a diagnostic finding of any significance - about 230 times more likely, in fact.