Friday, November 20, 2009

New guidelines for cervical (Pap Smear) screening

This seems to be the week for announcing new non-intuitive medical guidelines. My last three blogs focused on the November 16 mammography guidelines that recommended halting routine screening mammograms for women under 50.

Today (November 20, 2009), the American Congress of Obstetricians and Gynecologists (ACOG) announced their new guidelines for cervical (Pap Smear) screening. The major change is that the first Pap smear screening is now delayed until women are 21 years old. The prior recommendation was for women to get their first screening three years after they became sexually active, or age 21, whichever came first.

ACOG's official release statement , dated today, can be read at their web site. It's a short, one-page explanation, but it contains highly misleading statements.

Here's one: "Cervical cancer rates have fallen more than 50% in the past 30 years in the US due to the widespread use of the Pap test. The incidence of cervical cancer fell from 14.8 per 100,000 women in 1975 to 6.5 per 100,000 women in 2006."

Virtually every study of Pap smear screening shows a drop of at least 70% in the cervical cancer death rate, in populations that institute screening. I have no idea where they got the 50% number. The more disturbing part of their statement is the comparison of the U.S. cervical cancer death rate in 1975 with the death rate in 2006. This makes no sense.

If you want to measure the drop in the cervical cancer death rate before and after a screening tool has been implemented, you need to go back to a date preceding the introduction of the screening tool. In 1941, Papanicolaou and his coworkers published their paper establishing the diagnostic value of examining cervical smears to screen for cervical precancer. It took a while to implement the test nationwide, but it was certainly in common use in the 1960s. By the time 1975 came around, the Pap smear had already influenced the cervical cancer death rate. You should not be looking at the interim between 1975 and 2006 to measure the drop in cancer.

You've got to compare a pre-Pap date and a post-Pap date. The National Cancer Institute has done this for us. Cancer death rates for selected sites is shown for 1950 and 2005 in Table I-3. SUMMARY OF CHANGES IN CANCER MORTALITY, 1950-2005 AND 5-YEAR RELATIVE SURVIVAL RATES, 1950-2004 Males and Females, By Primary Cancer Site.

The table indicates that the cervical cancer death rate dropped 81.4% in white women. Furthermore, the uterine cancer death rate dropped 68.8% in the same 55-year period. Pap smears also screen for dysplasias and cancer of the endometrium (uterine lining), though with less sensitivity than for cervical screening.

That was not the only problem with the ACOG announcement. Another quotation is, "Although the rate of HPV infection is high among sexually active adolescents, invasive cervical cancer is very rare in women under age 21."

This statement gives the impression that the Pap smear is a screen for cervical cancer. It is not. The Pap smear is a screen for cervical precancer (referred to as dysplasias and CIN in the ACOG statement), not for cervical cancer, and the persons responsible for the ACOG statement don't seem to understand this. Precancers are the lesions that precede the development of cancer , and it may take precancers a decade or more to develop into cancers. Though the Pap smear can detect cervical cancers, the whole idea behind the test is to find precancers before they become cancers, when they can be treated by a simple excisional biopsy. The fact that cancers rarely occur in women under the age of 21 means that the neoplastic lesions most likely to be found by Pap smear in women under 21 are cervical precancers (i.e., the lesions that we're trying to find)!

The ACOG release also states: "Screening for cervical cancer in adolescents only serves to increase their anxiety and has led to overuse of follow-up procedures for something that usually resolves on its own."

Pap smear screening in adolescents actually has a number of useful purposes. It draws young women into the gynecologist's office, where a broad range of gynecologic diseases, in addition to cervical precancer, can be detected and treated. In fact, many infections of the vagina and cervix can be diagnosed by Pap smear. Their assertion that the Pap smear leads to over-use of follow-up procedures is also questionable. If there is an overuse of procedures following Pap smears (and I wouldn't know whether there is or isn't), then the ACOG should produce guidelines on the proper use of follow-up procedures. Reducing Pap smear screening in the under 21 age group because doctors do the wrong follow-up after they receive the smear report, seems absurd to me.

In summary, I don't really know whether the ACOG recommendations are any good. All I know is that some of the reasons that they provide in their release statement don't make much sense.

- © 2009 Jules J. Berman, Ph.D., M.D.

key words: cervical cancer, cin, dysplasia, precancer, precancerous lesions, hpv, Pap smear, Pap screening, cervical screening, cervical cancer screening, adolescents, teen-agers, screening test, new recommendations, new guidelines, early cancer screening, cancer death rate, task force recommendations, ACOG, precancers, early detection

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