UPDATE: CERVICAL DISEASE
Here’s what you need to know about ACOG’s latest guidelines on screening for cervical cancer
IN THIS ARTICLE
A study of the detection of squamous cell cervical cancer (SCC) within 3.5 years of one, two, or three consecutive normal Pap tests demonstrated that the incidence of cervical cancer increases to 3 to 5 cases for every 100,000 woman-years in each of the subsequent 2 years. Some experts argue that this relatively low increase—the equivalent of the incidence of breast cancer in men—supports extension of the screening interval to 3 years after three consecutive normal Pap results.
Clinicians have generally been hesitant to widen the screening interval, despite ACS and ACOG recommendations for 2- or 3-year screening among women who have had three consecutive normal results. Many of these clinicians may find it difficult to dismiss even this low number of excess cancers (3 to 5 cases for every 100,000 woman-years) when more frequent or better screening would likely prevent them. As a result, the extension of screening intervals on the basis of negative cytology alone may continue to meet resistance from clinicians and their patients.
Wider intervals reduce the risk of unnecessary treatment
The extension of screening intervals, whether it is based on cytology alone or cytology combined with HPV testing, benefits most women by reducing the likelihood that transient, HPV-induced events will be detected and treated even though they are not destined to become CIN 3, adenocarcinoma in situ, or cervical cancer.
At the same time, however, extending the screening interval to 3 years in the setting of “opportunistic” screening—the screening approach used in the United States—may lead to irregular screening for many women at intervals beyond the recommended 3 years, thereby reducing the protective effect of a program based on cytology alone. Approximately 10% of cervical cancers occur in women who have not had a Pap test in the preceding 5 years.
Cotesting may be the solution
There is no question that extending cytology-only screening beyond 3 years significantly increases the risk of cervical cancer. However, among women tested for HPV, the risk of CIN 3 or greater does not begin to rise until at least 6 years following a negative test result, providing a margin of safety that would protect most women who miss the recommended 3-year screening interval.
Earlier this year, Ronco and colleagues published the results of a large primary cervical screening trial involving more than 94,000 women who were randomly assigned to screening with cytology alone or cotesting (i.e., cytology plus HPV testing).4 In the cytology-only group, women were referred to colposcopy for a Pap result of ASC-US or higher-grade findings. In the cotesting group, they were referred to colposcopy if the HPV or Pap test (or both) was positive. A second screening was performed an average of 3 years later, and the incidences of CIN 2, CIN 3, and cancer at each screening were compared between groups.
The number of cancers detected in the initial round of screening did not differ between groups. In the second round of screening, no cancers were found in the cotesting group, compared with nine cancers in the cytology-only group. The authors attributed this difference to the detection and treatment of twice as many cases of CIN 3 in the initial round of screening among women undergoing cotesting, compared with those tested with cytology alone.4
In addition, women in the cotesting group had an extremely low rate of CIN 3 in the second round of screening (2 cases for every 10,000 women). Investigators also noted that a high proportion of invasive cancers detected in the cytology group during the second round of screening were adenocarcinomas, consistent with reports from earlier studies that found cytology to be less effective in detecting adenocarcinomas than in detecting SCC.4
Although HPV testing was previously shown to outperform cytology in reducing the risk of cervical cancer in a low-resource country (India), this is the first study to do so in a developed country with a well-screened population and a low incidence of cervical cancer.4
Although ACOG guidelines encourage the extension of screening intervals to 3 years for women 30 years or older who have had three consecutive normal Pap tests, many clinicians have been reluctant to take this step. Cotesting with HPV and Pap tests should provide the reassurance necessary for these clinicians to adopt the wider screening intervals.
Keep annual screening for women who have a history of CIN, HIV, or certain chronic conditions
The recommendations to screen women every 2 years until age 30 and to extend the screening interval to 3 years thereafter, provided three consecutive Pap tests are normal or cotesting is negative, apply only to women at average risk of cervical cancer. Conditions that indicate elevated risk include:
