Cervical intraepithelial neoplasia (CIN) has been traditionally defined as a continuum of intraepithelial squamous abnormalities which exhibit nuclear atypia in all epithelial layers and possess some potential for progression to invasive carcinoma if not removed. Efforts to subdivide this spectrum into categories of low and high cancer risk have been based previously on the strong association between CIN III (carcinoma in situ) and subsequent invaise carcinoma. However, in practice, this distinction has been discouraged because CIN I and II may be associated with CIN III and a small propation may progress to invaise carcinoma. As human papillomaviriuses (HPV) have emerged as potential markers for subdividing precursor lesion, so-called “high-risk” HPV types have been associated with all grades of CIN, whereas “low-risk” HPV types have segregated primarily in lesions closely resembling condylomata. The place of condyloma in the spectrum of CIN, as well as the precise definition of CIN I, has been controversial. Some authors distinguish condyloma from CIN I and others use similar criteria for the diagnosis of both. Currently, the trend among pathologists and cytopathologists is to classify CIN I, as a process either identical to or closely resembling condyloma (low-grade), and CIN II and III as lesions falling within the spectrum of CIN as classically described (high-grade).As new etiologic perspective (HPV), classifications (Bethesda) and outpatient mamagements (LEEP) evolve, morphologic definitions of CIN will remain important to patient care, particularly if managment decisions are based on nuances of histologic or cytologic grade. When using cervical lesion morphology as an end point in chemoprevention chemprevention studies, investigators must understand that “morophologic progression” of CIN may not be synonymous with biologic progression, that discrepancies between HPV type and morphology exist, and that cytology and histology provide variable, and at times conflicting, information.
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