The goal of all cervical cancer classification systems is to establish management guidelines that decrease the like-lihood of progression of precursor lesions to more advanced lesions. The 2001 Bethesda System is the most widely used system in the United States for reporting and classifying cervical cytologic studies. Established in 1988 and updated in 1991 and 2001, The Bethesda Classification outlines the various possible results of the Pap test, specifies accepted methodologies of reporting the Pap results, and provides for interpretation of findings. This categorization allows for defined management options regarding the initial results of the Pap test (Box 43.2).
The classification used by the Bethesda system divides epithelial lesions into two categories: squamous lesions and glandular lesions. In both categories, lesions are either precancerous or cancerous. Squamous precursor lesions are described as either atypical squamous cells (ASC),low-grade squamous intraepithelial lesions (LSIL) or high-grade squamous intraepithelial lesions (HSIL), while cancerous lesions are termed invasive squamous car-cinoma. ASC is further divided into ASC of undetermined significance (ASC-US), and ASC–cannot exclude HSIL (ASC-H). Precancerous glandular lesions are classified as atypical (AGC); atypical, favor neoplastic; and endo-cervical adenocarcinoma in situ (AIS). Cancerous glan-dular lesions are classified as adenocarcinoma. AGC is also classified as endocervical, endometrial, or not other-wise specified (NOS).
Before the intraepithelial lesion terminology was cre-ated, the term cervical intraepithelial neoplasia (CIN) was used, and lesions were graded as CIN 1, CIN 2, or CIN 3.
The CIN classification system replaced an even earlier classification scheme that used the term dysplasia and classified precancerous lesions as mild, moderate, or severe. With each revision, the terminology for cervical cancer results has become more precise and reflects the cur-rent scientific understanding of the progression of cervical cancer. The CIN terminology, however, is still used with the current Bethesda terminology. LSIL encompasses HPV infection, mild dysplasia, or CIN 1. HSIL encom-passes CIN 2 and CIN 3. CIN 3 is also designated carci-noma in situ (Table 43.1).
Despite decades of study, the natural history of cervi-cal intraepithelial lesions is still not completely understood.
The once widely held concept that low-grade lesions are necessary precursors to the high-grade lesions that, in turn, may progress to invasive cancer has been questioned as the sole pathogenesis. It has been observed, for example, that many women present with CIN 2 or CIN 3 without prior CIN 1 lesions. Although multiple longitudinal studies have attempted to document rates of “progression” and “regres-sion” of CIN, results of these studies must be interpreted with caution due to varying methods of diagnostic criteria, populations, and duration of follow-up.