HPV test detects cancer with 95% accuracy

Tuesday, April 7th, 2009

No one wants cervical cancer screening to be like flipping a coin.

A recent study revealed the human papillomavirus (HPV) test is more effective at detecting cervical cancer than traditional Pap smears.

The preliminary research of the Canadian Cervical Cancer Screening Trial (CCCaST) was led by Dr. Eduardo Franco, director of the Division of Cancer Epidemiology at McGill University’s Faculty of Medicine.

Dr. Franco’s study discovered the HPV test detects signs of cancer with an accuracy rate of 94.6 per cent without generating false results. The Pap test has an accuracy rate of 55.4 per cent, which Franco compared to “flipping a coin.”

The CCCaST’s results, published in The New England Journal of Medicine, offer an alternative to the Pap smear, which has been the standard test for cervical cancer for almost 50 years.

Both the Pap smear and HPV test require the collection of a cervical sample; the difference lies in the analysis of the sample, explained Dr. Peter Ainsworth, head of molecular diagnostics at the London Health Science Centre.

Pap tests analyze cells under a microscope searching for abnormalities, while the HPV test is automated and detects the DNA of high-risk HPV strains known to cause cervical cancer.

“The Pap smear is looking at dismorphisms [where] the cells take different shapes and don’t look normal,” Ainsworth said.

“This DNA test is actually looking for the viral genome of these two specific subtypes of [HPV] that cause [cervical] cancer. They have a specific DNA sequence.”

The study concluded although the sensitivity of the HPV test was almost 40 per cent higher than the Pap test, the latter is less likely to generate false positives.

In a press release, Dr. Franco noted while a false positive may be psychologically distressing for a patient, it is more desirable than a false negative " which could allow cancer to develop undetected.

Ainsworth said, the HPV test will likely be an add-on to traditional screening.

“You must be very cautious about adopting a test without being fully sure that it is doing the job the original test is doing,” Ainsworth said.

Dr. P.K. Lala, professor emeritus of anatomy and cell biology at Western, said the HPV test is powerful.

“But on the other hand, it’ll take time for the test to be readily available.”

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