Anne Paxton
January 2021—It’s a watershed moment when an influential standard-setting organization, the American Cancer Society, announces that a test widely used for decades should be supplanted—especially when the test is the linchpin of the most successful cancer screening program in U.S. history. But phasing out the Pap test and replacing it with human papillomavirus testing for primary cervical cancer screening is indeed the long-term objective of the ACS’ updated guidelines, released July 30, 2020.
In the short term, the ACS has designated HPV testing as the preferred primary screening test for cervical cancer. And that shift away from Pap testing—and even away from cotesting with Pap and HPV—is a matter of serious concern to the CAP and other members of the Cytopathology Education and Technology Consortium (CETC), for several reasons.
“A move to using primary HPV screening alone, without recommending the option of cotesting, is the single most important change affecting the field of cytopathology and pathology in general,” says Diane Davey, MD, who practices pathology at the Orlando Veterans Affairs Medical Center and is a professor of pathology and associate dean at the University of Central Florida.
The ACS recommends that individuals with a cervix be screened for cervical cancer from age 25 through age 65 using primary HPV testing as the preferred screening method and repeating every five years. Cotesting with HPV testing in combination with cytology is also labeled an acceptable option, but it would be acceptable only if primary HPV testing is not available.
By ACS estimates, switching to primary HPV testing starting at age 25 would prevent 13 percent more cervical cancers and seven percent more cervical cancer deaths than the previous strategy of starting Pap testing at age 21. The CAP, however, believes that the ACS recommendation poses significant risk to patients and gives short shrift to cotesting, which the CAP said in an Oct. 15 letter to the ACS should be continued as a screening strategy because it provides the sensitivity and specificity needed for all patients.
“They’re not forbidding cotesting,” says Dr. Davey, who is active in the American Society of Cytopathology and a former member and chair of the CAP Cytopathology Committee. She helped write the official response for the CETC, which represented the views of all of its member societies, on the case for cotesting rather than HPV as the primary screening test. “But what they are stating is that HPV primary screening is the preferred modality and they expect that clinical providers will be moving to that,” she says.
Most U.S. laboratories do not offer primary HPV screening on platforms approved by the FDA for that purpose, nor is HPV genotyping, a suggested modality for triage of a positive primary HPV test, widely available. One of the CAP’s main objections to the ACS guidelines—and an obstacle to their quick widespread adoption—is that fewer than half of laboratories in the U.S. perform primary HPV testing with the only two FDA-approved tests available—Roche Cobas and BD Onclarity. The widely used Hologic Aptima HPV assay is not approved for primary screening.
“Both the Cobas and Aptima have been around for a while and are good tests,” Dr. Davey says. But pathologists are concerned about the adequacy of the specimen to make sure that the lab is actually testing cellular material. “Some of the HPV platforms have control mechanisms to tell you that there’s human DNA in them, and that is one reason FDA approved them for that use. Not to say that Aptima couldn’t be adopted at some point; it’s an excellent test but hasn’t gotten that approval. But, to my knowledge, none of the tests can tell you if you’ve got the sample from the right place, which would be from the cervix, especially the transformation zone or mouth of the cervix where we see the most cancers and precursor lesions develop.”
The CAP commented to the ACS early on about the test platform issues, and in the final version of the guidelines released in July last year, the ACS “did acknowledge that it was important for providers to check with their laboratories to ensure they are using a platform approved for primary screening. We were very concerned about communication issues and clinicians thinking they could switch to primary screening and send their sample the same way they had in the past,” Dr. Davey says.
“That’s one of the barriers. It’s a huge access problem right now for a lot of women who have their HPV testing done using a variety of platforms. We do cotesting at the VA. We send out our HPV testing to a commercial laboratory and we use the Aptima platform. We’ve been very happy with its performance, but that’s as a cotest.”
“I think that the additive results from both tests are useful,” she adds. “If we get a positive HPV result and we didn’t see anything on the Pap test originally, we will go back and look at it again. It’s one of our quality control measures.” That does introduce a bit of bias, she admits. “But I think it’s best for patient care to consider both results together. It can give some advantages to patient management.”
[dropcap]A[/dropcap]nother CAP concern relates to the number of years of experience that pathologists and clinicians have with the Pap test. “HPV testing is a good test but we don’t have that long historical reference,” Dr. Davey says. “And we don’t have really organized screening programs as some countries do. In the U.S., screening is still considered opportunistic. If the woman is up to date with ‘well woman strategies,’ chances are they are getting screened properly. But there are still a lot of people who change providers, may be seeing someone just for a specific indication, or may not have good health care coverage.”
“There is definitely still a significant portion of the population that is not getting regular screening and those are some of the women who are still getting cervical cancer,” she continues. With the level of false-negatives HPV testing has, even though the test is considered very sensitive, “we are concerned that maybe the HPV test is missing something in women undergoing infrequent screening.”
That was why the CAP Cytopathology Committee considered it a “pretty abrupt move” when the ACS decided to allow for cotesting but only as an interim strategy until providers can work with laboratories that have a platform approved for HPV primary screening alone, Dr. Davey says. Other specialty groups have pushed back on the guidelines, and gynecology organizations like the American College of Obstetricians and Gynecologists have not yet adopted what the ACS is recommending.
The CAP supports the use of HPV vaccines. “But the vaccine doesn’t catch all of the HPV types that can cause cancer. It gets the most important types, but not all of them,” Dr. Davey says. Countries that adopt HPV primary screening are mainly ones with better vaccination programs and more uniform prevention strategies than the U.S. has. “And there’s less expectation that every cancer will be detected. In the U.S., women and providers have higher expectations, and we would like to still promote cotesting because we know that two tests done together have very good sensitivity.”
This is particularly important given the disparities among different racial and ethnic groups, she adds. “Some groups do better with vaccination, some do better with the screening, and some do poorly with both. We don’t want to miss any of them.”
Insurance coverage for cotesting is also a factor that could have a harsher impact on some groups. Lacking an organized national screening program for cervical cancer, the U.S. tends to underscreen women, especially those of lower socioeconomic status or minorities. “They are the hardest hit in general by infection rate,” Dr. Davey says. “So when the insurance company says, ‘We’re only going to pay for one test or the other, not for the cotest,’ we are concerned. We could see that happening. In many other countries where there is an organized screening program, there are fewer differences between screening and treatment for different groups. In this country, if you’re only having episodic health coverage, or it’s not high quality, that’s going to hit some segments of the population more than others.”
A final concern is that the HPV testing strategy requires that if a patient has a positive HPV test result, “usually you’ll take the rest of the specimen and do a cytology Pap preparation,” Dr. Davey says. “But when the HPV test is positive, some people are going right to colposcopy. And there’s not a lot of standardization in those strategies.” Although for now the pandemic has led to postponement of some colposcopies and other procedures, “those colposcopy clinics may get overwhelmed. We don’t have enough data yet. But I don’t think they’re as far along as laboratories in having standardized methods and quality assurance.”
As some skeptics about the shift to HPV screening suggest, there may have been similar problems with the microsimulation model that was instrumental in shaping the ACS guidelines. “A lot of the data is based on detection of precursor lesions, and not invasive cancers,” Dr. Davey says. “And there’s not been enough time to see, in a real-world setting, what will happen to cancer rates. What inputs are used as modeling parameters? Are they representative of all laboratories and the way women are getting testing in this country? We do have concerns. And some of the early pressure for HPV testing was not even based on any U.S. data. We do have U.S. data now, but a lot of it is from California, and that may also not be completely representative.”
[dropcap]F[/dropcap]or Dina Mody, MD, director of cytology laboratories at Houston Methodist Hospital and director of Texas operations for gynecology testing for BioReference Laboratories, the ACS recommendation to switch to HPV as the primary screening test runs counter to documented experience. The data tell the story, in her view.
In recent years, Dr. Mody noticed a pattern—“a big uptick in cotesting,” she says—at Houston Methodist and BioReference Laboratories, which conducted 214,000 Pap tests and had 59 primary HPV requests in 2019. The increase in cotesting brought to light some anomalies of interest. “As we ramped up, and our volume started increasing, we noticed as early as 2013 in both labs that there were cases of high grades and cancers that were testing negative with the HPV test. And we weren’t the only ones noticing that,” says Dr. Mody, who is a former chair of the CAP Cytopathology Committee.
Away from the academic groups at Houston Methodist Hospital, Dr. Mody says, the “real-world OB/GYNs” in Houston’s suburbs, East or West Texas, Hill Country, Austin, El Paso, “are not sold on HPV. They’re probably playing a wait-and-watch game, and they’re doing cotesting. They have enough lawsuits with the pregnancies and deliveries so they’re probably being careful. Ultimately, I don’t think many OB/GYNs are ready for primary HPV screening. There hasn’t been a groundswell of requests, at least not in Texas.” Another factor: “Some people have said that they want their patients to come back.” With testing at five-year intervals, “they may lose them, and then patients come back with a bigger medical problem or cancer.”
Because of COVID testing, for which the workhorses are the two platforms (Cobas and Panther) that are also used for HPV testing, there’s been increased awareness of false-positives—which run about 0.7 to 0.35 percent (from just carryover issues) with HPV testing—and false-negatives. The latter break out clearly in cotesting’s favor. False-negatives are nine percent with Pap testing and nine percent with HPV testing; they drop to one percent with cotesting (Zhou H, et al. Cancer Cytopathol. 2016;124[5]:317–323).
As the CAP said in its Oct. 15 letter to the ACS, “a considerable number of invasive cancers (9–10%) test negative for HPV” and “8.3–14% of HSIL may also yield negative hrHPV results with the currently available HPV tests.” Endocervical adenocarcinoma and adenocarcinoma in situ are other neoplastic processes that will be overlooked by instating primary HPV testing only, the CAP said.
BioReference’s test volume is highly monitored, and programmers and lab QA professionals on Dr. Mody’s team have been tracking the data on its testing each month, Dr. Mody says. “There’s somebody actually watching our numbers daily and it’s done in real time.” That data has been a gold mine, she says. It has not only given her team powerful content to publish but also allowed efficient comparisons with CAP data and data from sites in Florida and New Jersey where BioReference also performs testing.
Because the academic group that runs BioReference Laboratories in Texas consists of both cytopathologists and gynecologic pathologists who do cytology as well as interpret the biopsies, “we have a unique situation,” Dr. Mody points out. When a biopsy is done, “we pull the previous Pap that drove the biopsy and we look at it at the time of interpretation of the biopsy and say whether it does or doesn’t correlate, and if not, then why. The OB/GYNs like that because they know what the next step is for them.”
Like Dr. Davey, Dr. Mody points to the potentially unnecessary colposcopies that can result when use of HPV testing for screening increases. “Once we started offering cotesting, the number of colposcopies and biopsies started going up,” Dr. Mody says. “Of course that adds cost. And we did pick up a few more high grades, but the difference wasn’t statistically significant.”
Biasing of Pap test results can be an unfortunate side effect of cotesting. Studies have shown that once the HPV status in a patient is known, it’s more likely to affect the result of the Pap test. In her laboratory, “once the cytotechnologists know that the HPV is positive, they tend to bump up the result to ASC-US [atypical squamous cells-undetermined significance]. So we blocked the HPV result from the cytotechs doing the Pap screening,” Dr. Mody says.
“But we knew from an earlier study about the nine percent false-negative rate. So what we have done—and it’s easy to do—is adopt an algorithm. We see the nine percent negativity rate on the Cobas. So every time there is a high-grade Pap with a negative Cobas, that Cobas result is suppressed and it automatically reflexes to the Hologic Panther, which has half the negativity rate. If the Panther is also negative, then the Cobas result is unsuppressed and is released. But if the Panther is positive and the Cobas is negative, the Cobas result is suppressed and the Panther positive result is automatically reported. It costs the company more but is best for the patient.”
The other problem is that every time there is a positive HPV and negative Pap, as part of the CLIA’88 mandated prospective rescreening of negative Pap tests, “we have an algorithm that pulls those HPV-positive, Pap-negative cases into the QC pile. Now, even though the original cytotech didn’t know that this HPV test was positive, it goes to the QC tech, who does know, because those cases run 24 to 48 hours behind the regular 10 percent QC.” Hence they tend to bump specimens with positive HPV up to ASC-US. “That’s expectation bias, because they know about the HPV result. I tell them it’s picking up every transient infection and just because the HPV is positive, don’t call it ASC-US and send it in because most of these HPV infections are transient. There’s a minuscule percentage that go on to develop a high-grade lesion.” And even high grade doesn’t automatically mean cancer. “Yes, a third of them will get cancer if we follow them over the next 20 to 30 years, but the other two-thirds will regress or just stay the same. We know this because of the unfortunate study from New Zealand in the ’50s through ’70s.”
Cotesting costs more, but it allows the longer five-year interval between tests, Dr. Mody points out. “And if you’re going to go to a five-year interval, I would rather have the cotests, knowing what I know in my population with the nine percent false-negative HPV rate on high grade and cancers. In Texas, where there is a large immigrant population most of whom have never been screened, I would feel more comfortable if they had the double test for at least the first two or three rounds. And, after two rounds of double negatives, maybe you can go to HPV alone every five years.”
[dropcap]S[/dropcap]ince SARS-CoV-2 testing tends to be performed on the same instruments as HPV testing, using the same pipette tips and other reagents and hardware, HPV testing has tended to bump up against supply shortages during the COVID-19 pandemic. “Even though we’re a large commercial lab and a large Texas medical center lab, when the tips came in, they went to the molecular lab doing the COVID testing. At one time, during that second peak of COVID, we had a three-week backlog for HPV tests,” Dr. Mody says.
The turmoil of this pandemic year has helped create not only shortages but a general climate of uncertainty about the directions many types of screening will take. “We know this is a time of change,” Dr. Davey says. “We don’t know how widely the guidelines will be adopted and how long it will take providers like gynecologists and family medicine doctors to adopt them. In the meantime, we’ve got some HPV testing platforms that are not approved for primary screening, and we need to work very closely with our providers to make sure we’re offering testing that is appropriate.”
As Dr. Mody notes, there is no perfect test. “Each test has its false-positives and false-negatives. If you do two tests in combination, you’re less likely to miss anything. And it gives you a bit more security,” she says, “especially with extended screening intervals. With an underscreened or never-screened population, it’s all the more important to go, at least for the first couple of rounds, with the dual tests before you say ‘Okay.’”
Anne Paxton is a writer and attorney in Seattle.