Review of ASCUS Pap Smears
Special Feature
Review of ASCUS Pap Smears
By Kenneth L. Noller, MD
The bethesea system (tbs) for pap smear reporting introduced the term "Atypical Squamous Cells of Undetermined Significance" (ASCUS) for the first time. The category was initially confusing to both clinicians and cytopathologists, as the older Pap System had not included a category for "I don’t know." Indeed, there had always been Pap smears with minor abnormalities that had puzzled cytologists. In the Pap system they were forced to place them in the "Class II" category which was a mixture of infections, inflammation, repair, and questionably neoplastic cells. With the introduction of TBS, pathologists now had a category in which to place only those smears which were slightly suspicious for neoplasia, but did not include sufficient features to categorize them as low grade squamous lesions. While I believe the introduction of this category makes good sense, and was an improvement over the Pap system Class II category, it is unfortunate that it was introduced without pretesting. Clinicians had no idea what to do with such reports.
Some time ago, TBS supported reporting ASCUS smears with a statement from the cytopathologist that the smear was most likely the result of either a benign or a neoplastic process. While some laboratories have reported relatively good results when the ASCUS category is so divided, others have found the subdivisions to be artificial and misleading. Clearly, a more objective delineation of the neoplastic potential of the cells seen on an ASCUS smear has been needed.
The first, preliminary results of the NCI-funded prospective randomized study of women with low grade and ASCUS cytology reports (the ALTS trial) have recently been reported at the biennial meeting of the American Society for Colposcopy and Cervical Pathology. Women were admitted to the trial only if they had a smear indicating either low-grade changes or ASCUS.
Each study participant had cytology, HPV testing, cervicography for documentation, and either follow-up cytology or colposcopy. The report at the ASCCP meeting concerned only those patients who had ASCUS reports. Based on early results, the investigators reported that it appears that HPV testing might be useful in the evaluation of ASCUS smears. Specifically, for those women who have an ASCUS cytology report but not those with LGSIL or HGSIL reports, HPV testing may be appropriate triage. Those women found to have an infection with a low-risk HPV subtype (about 40%) can be returned to annual screening without colposcopy or other testing, while those women with a high-grade HPV subtype (about 60%) should have colposcopy performed with biopsy as indicated. (See Figure.)
Algorithm for the evaluation of ASCUS reports
If the final, published results of the ALTS trial confirm this preliminary report, it would represent, in my opinion, the first clinically useful indication for HPV testing. However, there are some caveats. First, because HPV testing is relatively expensive it would not be cost effective to test all cytology samples. Rather, the laboratory should perform the testing only on those samples that result in ASCUS reports. Secondly, because office visits are also relatively expensive the sample for both cytology and HPV testing need to be collected at the time of the initial office visit and sent to the laboratory. The laboratory would then perform viral testing only on those samples from those women whose smears were reported as ASCUS.
There are at least two ways this system could be implemented. The clinician could obtain a traditional cytology sample and a separate sample for HPV testing and submit both to the laboratory. Alternatively, the clinician could use a liquid-based collection system which can be used for both cytology and HPV testing. In either case, considerable additional work will be placed on the laboratory, as they will need to maintain samples for a longer period of time—at least until the cytology report is finalized. At that point, those HPV samples from women whose smears were negative, or show LGSIL or HGSIL changes could be discarded and only those with ASCUS reports tested for HPV.
I strongly suspect that we will all be following the algorithm shown in the figure (or some modification of it) in the near future. However, strict adherence to the role of HPV testing will be necessary, as we must use our precious healthcare dollars appropriately. Universal HPV testing or colposcopy, or even repeat office visits to obtain an HPV sample, might add so much expense to the process of screening for cervical cancer that we would be forced by payers to abandon yearly screening.
References
1. The Bethesda System for reporting cervical/vaginal cytologic diagnoses: Revised after the second National Cancer Institute Workshop, April 29-30, 1991. Acta Cytologica 1993;37(2):115.
2. Solomon D. What have we learned from ALTS: Is it possible to eliminate ASCUS? Meeting of the American Society For Colposcopy and Cervical Pathology, Orlando FL, March 16, 2000.
3. Manos MM, et al. JAMA 1999;281:1605-1610.
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