Role of Pap Smears
The Pap smear is intended to detect changes in cellular morphology that are precursors to carcinoma. Because these morphologic changes, termed dysplasia, precede the development of cancer by 2 to 15 years, the incidence of death from cervical cancer should be reduced by detection of dysplasia by Pap smear and by subsequent treatment. In fact, this has been confirmed: In an unscreened population, 4/1000 deaths were caused by cervical cancer, while in an otherwise similar but screened population, the rate was 0.5/1000.
Human papillomaviruses (HPV) are thought to cause virtually all cervical dysplasias and carcinomas. (See box, "Biology of HPV Infection and Oncogenic Exposure.") There are more than 60 known HPV types, of which more than 10 infect the genital tract. Oncogenic exposure to HPV generally occurs in the 2nd and 3rd decades of life, dysplasia is most often found in the 3rd and 4th decades, and cervical cancers are most common in the 5th and 6th decades.
Most studies of recent Pap smear history in women who have invasive cervical cancer show that at least 50% have not undergone a Pap smear in the preceding 5 years. In the remainder of cases, Pap smears were performed that were more or less evenly divided between abnormal and normal readings (false negatives).[5,6,7] The false-negative rate of the Pap smear is at least 20%. This means that biopsy is imperative for visible cervical lesions. The use of serial Pap smear screening decreases the false-negative rate; with repeated smears, the probability of false negative equals (0.2)n, where n = number of Pap smears. Therefore, the probability of a false negative after 3 consecutive Pap smears is 0.2 x 0.2 x 0.2 = 0.008, or 0.8%.
False-negative Pap smears may result from a lesion that sheds few, if any, cells from inadequate sampling because of the location of the lesion (i.e., endocervix), from artifacts or poor preparation of slides, or from reading (interpretive) errors. Although most of these factors cannot be controlled by the clinician, Pap smears can be optimized by following a standardized routine (Table I).
Medscape General Medicine. 1996;1(1) © 1996
Cite this: Management of Abnormal Cervical/Vaginal Pap Smears - Medscape - Mar 29, 1996.