The use of biomarkers for characterizing HPV infections and diagnosing cervical cancer precursors has become a central topic in cervical cancer screening. Our study focused on p16 known as a marker for high risk HPV-infection that is expressed in 100% of lesions with CIN2 or higher and on Stathmin (Oncoprotein18, STMN), a marker that might be correlating with higher severity of intracervical lesions. The strength of expression of STMN over p16 might be an indicator for risk of dysplasia within a high-risk HPV infection and therefore serve as a good predictor for the severity of a lesion.
In a quantitative molecular assay we compared levels of mRNA expression of p16 and stathmin. This method is a multiplex assay combining specific mRNA capture and signal amplification with multi-analyte profiling beads (xMAP) technologies to simultaneously detect and quantify RNA targets. This allows a quantitative analysis. Values are arbitrary mean fluorescence intensity (MFI). P16 and STMN were divided by the MFI value for Actin β as a housekeeping gene and therefore put in relation to the absolute cell number.
A total of 178 cervical smears conserved in Thinprep were analysed. HPV genotyping (with multiplex human papillomavirus genotyping (MPG) and a Luminex read-out) was performed as part of the clinical diagnostics and clinical data for cytology, colposcopy and histology were used for classification of the lesions.
We found a median expression of p16 mRNA of 18.22 for samples with no cervical lesions (NILM, n=52), 6.42 for CIN1 (n=13), 19.03 for CIN2 (n=29), 25.31 for CIN3 (n=69) and 79.08 for invasive carcinomas (n=15).
Median expression of STMN mRNA was 20.74 for samples with no cervical lesions (NILM), 20.33 for CIN1, 19.27 for CIN2, 51.70 for CIN3 and 291.20 for invasive carcinomas.
We found an average ratio for STMN/p16 mRNA expression of 1.64 for patients with no cervical lesion (median: 0.8, standard deviation (SD): 2.03), 2.25 for CIN1 (median: 1.42, SD: 2.15), 1.43 for CIN 2 (median: 0.6, SD: 1.8), 4.61 for CIN3 (median: 1.67, SD: 10.77) and 12.91 for invasive carcinomas (median: 6.89, SD: 17.60).
While p16 is an indicator for high risk HPV infections, STMN shows a stronger increase of expression in CIN3 +. The ratio of STMN/p16 might therefore discriminate low risk of transformation and high grade dysplasia within lesions with hr HPV infection. This information could be of value in HPV diagnostics and can not yet be retrieved from other testing methods.