T he term atypical squamous cells of undetermined significance (ASCUS) was introduced in the Bethesda System to provide a designation for smears showing changes equivocal for a squamous intraepithelial lesion (SIL). 1 When introduced a decade ago, many pathologists and gynecologists hoped that ASCUS would be used sparingly to designate changes interpreted as equivocal human papillomavirus (HPV) effect. However, ASCUS proved to be the Pandora's box of cervical carcinoma screening, revealing all of the problems of routine clinical practice. It immediately became apparent that ASCUS was irreproducible and undefined, leaving gynecologists and their patients groping in the dark for appropriate management strategies. Although criteria were subsequently proposed and illustrated for ASCUS, 2 the category defied reproducible definition, and identifying a "gold standard" for the category has proved elusive. Specifically, reliance on reported histopathologic outcomes for women with ASCUS is problematic because standardized criteria for colposcopy referral and management are lacking 3 and colposcopic assessment and biopsy placement may vary, even among experts. 4 Finally, crosssectional studies reported from single institutions cannot account for the variation in many aspects of clinical practice among institutions and do not provide systematic follow-up for untreated women with mild HPV infections.
Use of ASCUS and Implications
Estimates suggest that there are 2-3 million smears diagnosed as ASCUS each year in the U.S. compared with about 15,000 invasive