Histopathologic extent of cervical intraepithelial neoplasia 3 lesions in the atypical squamous cells of undetermined significance low-grade squamous intraepithelial lesion triage study: implications for subject safety and lead-time bias.

Cervical intraepithelial neoplasia 3 (CIN3) is the precursor of mostsquamous carcinomas and serves as a surrogate end point. However, small CIN3 lesions are rarely associated with concurrent invasion. We hypothesized that aggressive follow-up for cytology of atypical squamous cells of undetermined significance (ASCUS) or low-grade squamous intraepithelial lesion (LSIL) leads predominantly to detection of smaller CIN3 lesions than those usually associated with cancer. We assessed this hypothesis in a masked histopathologic review of 330 CIN3 lesions in the ASCUS LSILTriage Study, focusing on ASCUS referrals. ASCUS referrals underwent randomized management [colposcopy for repeat cytology of high-grade squamous intraepithelial lesion (HSIL), colposcopy for oncogenic human papillomavirus (HPV) detection or repeat HSIL, or immediate colposcopy]; then all were followed with repeat cytology for 2 years, followed by colposcopy and aggressive treatment. We assessed all CIN3 lesions qualitatively and measured 39 of them. CIN3 lesions were overwhelmingly small. Compared with enrollment, lesions found at follow-up or exit involved fewer tissue fragments (P < 0.01) and showed less diffuse gland involvement (P = 0.03). CIN3 lesions found postenrollment after HPV testing involved the fewest tissue fragments [versus immediate colposcopy (P = 0.04) or repeat cytology of HSIL (P = 0.02)], and none showed diffuse gland involvement. The median distal-proximal length was 6.5 mm (median replacement of total epithelium = 5%) in the 39 measured cases. We conclude that CIN3 lesions underlying ASCUS or LSIL generally lack features associated with invasion, particularly if managed using HPV testing, suggesting that aggressive management leads to early detection of CIN3 but probably prevents relatively few cancers in screened populations.