Prediction of clinical outcome using p16INK4a immunocytochemical expression in low-grade squamous intraepithelial lesions and high-risk HPV-positive atypical squamous cells of undetermined significance in patients with and without colposcopic evident cervical disease

p16INK4a as a diagnostic marker of a cervical intraepithelial neoplasia of grade 2+ (CIN2+) in atypical squamous cells of undetermined significance (ASC-US) and low-grade squamous intraepithelial lesion (LSIL) cytological samples has been analyzed, but has not yet been included in clinical routine practice. One hundred and ninety-one patients with an abnormal Pap test (84 ASC-US and 107 LSILs) who underwent colposcopy were selected for this study. At enrollment, 96 patients (Group 1) had a positive colposcopy and therefore underwent a cervical biopsy, while 95 (Group 2) had a negative colposcopy and were followed up for up to 1 year. Both groups were tested for p16INK4a using immunocytochemical methods, and the p16INK4a results were correlated with histology or follow-up outcome. In Group 1 ASC-US cases, 82% of lesions less than CIN2 were p16INK4a-negative and all CIN2 cases were p16INK4a-positive (p=0.00044). In Group 1 LSIL cases, 71% of lesions less than CIN2 were p16INK4a-negative and 87% of CIN2/3 were p16INK4a-positive (p=0.00033). Seventy-seven percent of Group 2 ASC-US patients with a negative 1-year follow-up (NF-U) were p16INK4a-negative at enrollment, while all patients with positive follow-up (PF-U) were p16INK4a-positive (p=0.00113). In Group 2 LSIL cases, 83% of patients with NF-U were p16INK4a-negative, while 65% of patients with PF-U were p16INK4a-positive at enrollment (p=0.0014). In fact, 39% of the positive p16INK4a LSIL patients had CIN2+ histological lesions. The positive predictive value of p16INK4a for CIN2+ was 50% in ASC-US and 52% in LSIL cases; the negative predictive value was 100 and 94%, respectively. In conclusion, in our patients, a negative p16INK4a appears to be a marker of the absence of CIN3, while a positive p16INK4a can be correlated with the presence of histological CIN2+ found at enrollment or during the subsequent follow-up. Thus, its clinical predictive value is independent from the colposcopic aspect at enrollment.