Simplification of the new Bethesda 2001 classification system.

In 1989, a National Cancer Institute workshop resulted in the development of the Bethesda System for cytologic reporting of Papanicolaou smears. In the Bethesda III System (2001), potentially premalignant squamous lesions fall into 3 categories: Atypical squamous cells (ASC), low-grade squamous intraepithelial lesions (LGSIL), and high-grade intraepithelial lesions (HGSIL). The ASC category is subdivided into 2 categories: Those of unknown significance (ASC-US) and those in which high-grade lesions must be excluded (ASC-H). Further revision included the elimination of the category "benign cellular changes," which is now referred to as "negative for intraepithelial lesion or malignancy." The revision also refined the criteria for abnormal glandular epithelium, including atypical glandular cells (AGC). The principal modification in the updated system is the revision of the ASC category, which was done to facilitate triage of women for more intense screening when a true suspicion of a high-grade lesion was present.