Objective: To analyze follow-up data on atypical squamous cells of undetermined significance (ASCUS) based on morphologic characteristics.
Study design: Five years of follow-up was obtained on a cohort of 437 consecutive patients from 1986 who had initial diagnoses of ASCUS, with a further categorization of type based on the maturity of the atypical cells. All such categorizations were made on the basis of specific cytologic criteria. Follow-up cytology and/or biopsy was available on 366 patients.
Results: During the follow-up period, 40 patients (13.5%) with ASCUS were diagnosed as having a squamous intraepithelial lesion (SIL); 15 (5%) were interpreted as high grade. When stratified by type of ASCUS based on cellular maturity, the following association/progression rates were noted: mature ASCUS, 10%; metaplastic ASCUS, 24%; and immature metaplastic ASCUS, 42%. In metaplastic and immature metaplastic ASCUS cases, high grade SIL accounted for 42% and 60% of those subsequently diagnosed with a squamous intraepithelial lesion, respectively, versus 30% for mature ASCUS.
Conclusion: With well-defined and consistent criteria for the diagnosis of the variety of "squamous atypias," a stratification of risk of progression to or association with SIL can be made. When features of metaplasia and immature metaplasia are noted in the cells of ASCUS, patients were observed to be at increasingly greater risk for the detection of SIL; those cases were proportionately more likely to be high grade.