A test for HPV detects precancerous changes of the cervix earlier and more accurately than the Pap smear, according to a large clinical trial published Tuesday.

The randomized, controlled study — the kind of trial considered the “gold standard” of research — is the biggest, most comprehensive trial evidence that the human papillomavirus test is more sensitive than the Pap smear, a widely used test that has been a standard part of women's preventive health care for decades.

HPV’s role in cervical cancer

The HPV infection is the most common sexually transmitted infection and is usually eliminated by the immune system within a year or two. But when an infection persists, it can cause cellular changes that develop into precancerous lesions and, eventually, malignancies. Almost all cases of cervical cancer are caused by HPV infections.

About 13,240 new cases of invasive cervical cancer will be diagnosed in the United States in 2018, according to the American Cancer Society. About 4,200 women will die of the disease.

What could change after the study

Several experts predicted the results would spur efforts to entirely replace the Pap test with the HPV test.

Most medical groups have recommended that women in the United States get both the HPV test and the Pap smear — a practice called “co-testing.”

Now, armed with the new and previous studies, some experts say the Pap smear should be dropped.

Kathleen Schmeler, a gynecological oncologist at MD Anderson Cancer Center who was not involved in the study, was enthused about the new results. “It’s fantastic,” she said. “What this shows is that you could potentially do just the HPV test and move toward getting rid of the Pap test.”

But others disagree, saying that the Pap smear can catch a small number of cases of abnormal cells that might be missed by the HPV test and that co-testing should continue.

Many of the medical groups have said that before moving to HPV testing only, they needed to see clinical trial results — such as the kind provided by the new head-to-head study — to determine which test, over time, was better at detecting the precancerous changes. These conditions can be treated before they progress to cervical cancer.

Mark Spitzer, a gynecologist in New Hyde Park, N.Y., and past president of the American Society for Colposcopy and Cervical Pathology, said that although the study confirmed previous research showing that the HPV test is more sensitive than the Pap test, it didn’t answer a critical question: Is the HPV test alone better than the HPV test and the Pap smear together, as is current practice?

In the United States, the conventional Pap smear has been largely replaced by a liquid-based Pap cytology test. Cervical cells for both the Pap and HPV tests can be collected at the same time, during a pelvic exam.

Current recommendations for ‘co-testing’

• The American Cancer Society and the American College of Obstetricians and Gynecologists recommend that women of average risk get both HPV tests and Pap smears every five years between age 30 and 65, though they say a Pap test alone every three years is an acceptable alternative.

• Women in their 20s are advised to get Pap smears, not HPV tests, because the virus is so common that most would test positive for infections that would most likely clear up on their own.

• The United States Preventive Services Task Force, an independent panel that reviews the evidence of effectiveness for preventive services, currently recommends the “co-testing” for signs of cervical cancer that other groups advocate. Last fall, it issued a draft recommendation proposing that women undergo either HPV testing every five years or Pap smears every three years, but a final recommendation has not been released.

About the study

The decade-long study, which appeared in JAMA, involved about 19,000 women who were placed in two groups: one using the HPV test to screen for cervical cancer; and the other using Pap cytology.

In 2017, the researchers running the study reported that there were significantly more cases of precancerous lesions detected early in the trial among the women in the HPV-tested group, compared with the Pap cytology group.

Tuesday’s report detailed the “exit” results of the study 48 months after the women were enrolled and first screened. For those final results, both groups were tested using both the HPV test and the Pap test.

The researchers reported that there were fewer cases of precancer in the HPV test group, compared with the Pap smear group. That’s because cases of worrisome cellular changes already had been detected and dealt with after the women were first screened, said lead author Gina Ogilvie, a physician and public health researcher at the University of British Columbia. “The real benefit of co-testing is with the HPV test,” she said.

The report noted that adding HPV test to the Pap test group resulted in finding 25 lesions that would have not been found by the Pap test alone. By adding the Pap test to the HPV group, an additional three lesions were found.

Spitzer said those three cases support the “small but significant benefit of co-testing.”

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