Co-Localization of p16INK4a and MIB-1 Distinguishes High Grade Premalignant Lesions from Tuboendometrial Metaplasia in Cervical Mucosa
PN Samarawardana, KR Shroyer. Stony Brook University Medical Center, Stony Brook, NY
Background: The histologic diagnosis of high grade premalignant squamous and glandular lesions of the uterine cervix is problematic in cases that have morphologic overlap with benign changes. p16INK4a, a surrogate marker of HPV integration into the host genome, is overexpressed in CIN, AIS, carcinoma, and in tuboendometrial metaplasia (TEM), but not in benign proliferative lesions. MIB-1 is also overexpressed in CIN, AIS, carcinoma, and in some benign proliferative lesions, but not in TEM. Since TEM has a low proliferative rate, the current study was designed to test the hypothesis that the co-localization of p16INK4a and MIB-1, but not the localization of either marker in isolation, specifically detects clinically significant cervical lesions.
Design: Formalin-fixed cervical biopsy specimens, representative of 260 diagnostic regions, were subjected to two color immunohistochemical staining for p16INK4a (MTM labs AG) and MIB-1 (VectorLabs) using an EnVision polymer based method (Dako). The chromogen combination of DAB-brown for the detection of p16INK4a and alkaline phosphatase-blue for MIB-1 exhibited good color contrast in the distinction of these two antigens. Histologic regions were scored positive for either marker based on the detection of p16INK4a or MIB-1 in greater than 10% of the cells of interest.
Results: Positive test results with co-localization of p16INK4a/MIB-1 were found in 20/40 cases of CIN I (n=40) and in all cases of CIN II/III (n=32), squamous cell carcinoma (n=11), AIS (n=10), and invasive adenocarcinoma (n=8). Co-localization of p16INK4a/MIB-1 was also detected in 1/19 sections with TEM but was not detected in normal squamous mucosa (n=78), normal endocervical mucosa (n=72), or in microglandular hyperplasia (n=9). Sporadic staining for either p16INK4a or MIB-1 in isolation was detected in 14 sections of benign endocervical mucosa.
Conclusions: These findings demonstrate that the co-localization of p16INK4a and MIB-1 is more specific than either marker alone as a diagnostic adjunct for benign, premalignant, and malignant lesions of the cervical mucosa. Two color multiplex detection of p16INK4a and MIB-1 appears to overcome the problem of p16 expression in TEM as a potential source of false positive classification of test results. These observations highlight the utility of this approach for the classification of biopsy specimens and also suggest that a two-color immunocytochemical approach could be useful as a diagnostic adjunct for cervical cytology specimens.
Monday, March 9, 2009 1:00 PM
Poster Session II # 139, Monday Afternoon