The significance of “low-grade squamous intraepithelial lesion, cannot exclude high-grade squamous intraepithelial lesion” as a distinct squamous abnormality category in Papanicolaou tests

Abstract

Early cytologic detection and treatment of high-grade squamous intraepithelial lesion (HSIL) is critical to cervical cancer prevention. The term atypical squamous cells (ASC), cannot exclude HSIL (ASC-H) was introduced in 2001 in the Bethesda System (TBS 2001) to define changes suggestive, but not diagnostic, of HSIL in the absence of unequivocal squamous intraepithelial lesion (SIL). Previous studies showed that women with ASC-H cytology are at an increased risk of harboring underlying histopathologic HSIL. TBS 2001, however, did not address the significance of finding ASC-H changes in a background of unequivocal low-grade SIL (LSIL). There may be a tendency for cytologists to lump these changes with either LSIL or HSIL, depending on their level of comfort. In their laboratory, the authors have referred to these changes as "LSIL, cannot exclude HSIL" (LSIL-H). Between July 2001 and July 2003, all Papanicolaou (Pap) tests that were obtained by using the ThinPrep technique were retrieved from the computer data base at the authors' institution. All categories of squamous cell abnormalities, including LSIL-H, were evaluated for their incidence and follow-up diagnoses of HSIL and more severe lesions (HSIL +). All patients had a minimum of 2 year follow-up by biopsy and cytology (range, 2-4 years). LSIL-H comprised 0.15% (n = 194) of all Pap tests (n = 129,911) that were evaluated during the study period. Follow-up biopsy was available on 59 patients (30.4%), which showed HSIL + in 40.7% of patients. This rate of associated HSIL + differed significantly from that of LSIL (13%; P < .001) and HSIL (74%; P < .001), but was similar to that of ASC-H (44.6%). The results from this study showed that patients with cytologic diagnoses of LSIL-H had an intermediate risk of harboring histopathologic HSIL +. This risk was similar to ASC-H but fell between the low risk associated with ACS-US and LSIL and the high risk associated with HSIL cytologic diagnoses. The authors believe that LSIL-H should be considered as a distinct cytologic diagnostic interpretation and should be separated from LSIL and HSIL. Although LSIL-H does not represent a unique biologic entity, it has clinical usefulness because of its high positive predictive value for HSIL + lesions.