The Lady Doth Co-Test Too Much, Methinks

Adult women are very familiar with the Pap smear – an unpleasant necessity in the name of preventing cervical cancer. Once the sample is taken, cells are microscopically examined for morphological abnormalities that indicate a precancerous state. Ideally, any patient whose cells show such indications can then be treated for the condition before it progresses to cancer. But the Pap test is not infallible, and many factors can lead to a false negative result.

Current guidelines recommend co-testing using both the Pap smear and human papillomavirus (HPV) testing every five years – but given rising costs, co-testing may be an unsustainable approach. What if there were a more sensitive way to detect precancers than Pap testing alone? That’s the question a research team at the National Institutes of Health’s National Cancer Institute asked themselves, seeking a way to reduce the incidence of a cancer that affects over half a million people worldwide every year (1). To find out, they quantified the differences in cervical cancer detection rates between co-testing and HPV testing alone – and came up with a surprising result.

HPV testing demonstrated a clear superiority to cytology, identifying significantly more patients with either precancer or overt cancer. Did the Pap smear catch any cases missed by HPV testing? Very few, according to the study results – only 3.5 percent of precancers and 5.9 percent of cancers, translating to five cases per million screens in a year at most. The authors’ conclusion? That co-testing isn’t necessary; very few patients benefit from the addition of cytology. The most cost-effective option, the results suggest, is to forgo the Pap smear and focus solely on HPV testing for the future prevention and detection of cervical cancer.