New Pap Smear Technologies Promise Improved Sensitivity

SAN FRANCISCO—The Pap smear has long been one of the great success stories of gynecologic oncology. In the 50 years it has been used, it has reduced the death rate from cervical cancer by 70%.

Now several new technologies hold promise for catching more cervical abnormalities than ever before, Patricia Brawley, MD, professor and chief of the Division of Gynecologic Oncology, Louisiana State University, told Oncology News International. Dr. Brawley spoke by phone during her appearance at the 30th Annual Meeting of the Society of Gynecologic Oncologists (SGO).

“Although the traditional Pap smear is now a widely accepted technology, there is still room for improvement,” Dr. Brawley said. Statistics tell the story: 50% of women with cervical cancer have had a Pap smear within the last 3 years. Yet studies show that the sensitivity of the traditional Pap smear is just 51%. “The reason the Pap smear picks up cervical cancer so often is that this disease is a slow-developing abnormality,” Dr. Brawley said. “And in many women, the test is repeated fairly often.”

The FDA has approved three new Pap smear technologies. They include ThinPrep, a test in which cells are collected off the cervix and then put into a vial of fixative. The other two are computerized screening tests used with the traditional Pap smear (Papnet and AutoPap). Computerized screenings enable scientists to catch abnormal cells that would have been missed by the human eye. ThinPrep has at least one advantage: It has been shown to decrease the false-negative rate by 60%.

“The good thing about ThinPrep is that it addresses all the reasons why we have false negatives,” Dr. Brawley said. “When we use a slide, sometimes all the abnormal cells don’t get on. With ThinPrep, we’re increasing the number of cells that are available for screening because we collect them into a vial.” These cells are more representative, she added.

Cervical cells collected with ThinPrep are also more easily broken up, she said. It is easier to remove blood and inflammatory cells from clumps of cervical tissue. And that makes the cervical cells easier to interpret.

Another problem with the conventional Pap smear is that often the collected cells are not well preserved. ThinPrep, however, makes it easier to preserve cervical cells.

Atypical Squamous Cells

The conventional Pap smear does not allow accurate interpretation of atypical squamous cells. “Ten percent of all conventional Pap smears turn up these cells,” Dr. Brawley said. “Most patients within that group have no problem. But in 20% of that group, we’ll find a preinvasive lesion,” she said.

Physicians often struggle over what to do when a Pap smear finds these atypical squamous cells but cannot reveal if the cells are preinvasive. “There’s a huge number of patients who have these minimally abnormal cells. And doctors find it hard to decide if they should do a colposcopy. It’s costly and uncomfortable. In today’s legal climate, doctors often have a lot of anxiety about what to do. Their dilemma is that there is a small number of women with real abnormalities buried within a large group of these patients,” she said.

The good news, Dr. Brawley said, is that ThinPrep decreases the number of atypical cells found in smears. “It’s just a more accurate test,” she said.

Increased Cost

Unfortunately, not all obstetrician-gynecologists offer these new tests. The cost of the new Pap smears are, in fact, a point of contention. The new Pap smears add $15 to $25 to the cost of the Pap smear. And many laboratories are already losing money doing the traditional Pap smear. “A Pap smear now costs $10. So using the new technologies doubles or triples the cost,” Dr. Brawley said. “Still many health plans already cover the cost,” she added.

Another difficulty with the new technologies is that pathologists and technicians have to be retrained to use them. The retraining takes about a week, but not all labs are willing to bear the brunt of the cost. Many national commercial labs, however, are starting to offer the new tests.

The real question for many physicians, however, is whether the survival rate for cervical cancer will increase with use of the new Pap smears. “The American College of Obstetricians and Gynecologist has, in fact, taken a position that the new Pap smears shouldn’t be accepted as a standard of care until they’re proven in prospective studies,” Dr. Brawley said.

But that kind of study would be almost impossible to conduct, she added. “We would have to follow a huge number of women because the death rate from cervical cancer is so low. And it’s not ethical to do such a study in which you would be denying some women advanced technologies,” Dr. Brawley concluded.