The utility of p16^Ink4a/Ki-67 dual immunostain to triage women with Hr-HPV positive and negative Pap smear results (NILM) in Harare, Zimbabwe

Abstract

Background: Women who test Hr-HPV+/NILM have a 3-7% risk harboring of undetected underlying precancerous cervical lesions. The biomarkers: p16 ink4a and Ki67 are surrogate markers of cell-cycle dysregulation mediated by transforming HPV infections. Therefore, the p16 ink4a /Ki67 dual immunostain can be used to identify women with transforming HPV infections; these women have a higher risk of harboring undetected cervical precancerous lesions. Objectives: (1) To determine the proportion of women with prior Hr-HPV+/NILM screening results who are positive for p16 ink4a/Ki67 dual immunostain. (2) To compare Hr-HPV persistence rates between women with positive and negative immunostain results after 12 months. Design: Cross sectional descriptive study. Setting: Cimas Medical Laboratories and Parirenyatwa Central Hospital Laboratory. Subjects: Residual LBC samples from women with prior HR-HPV+/NILM results. Materials and Methods: Cell blocks were prepared from the residual LBC samples using the plasma-thrombin method. A paraffin serial section was cut from the cell blocks and stained manually with a mix of two monoclonal antibodies against p16Ink4a and Ki-67 proteins using the CINtec PLUS kit. The slides were evaluated using the binary rating score system: positive or negative. Follow-up Hr-HPV persistence rates were compared using an independent t-test. Results: Of the 82 residual LBC samples evaluated: 17.1% [14/82] were positive and 82.9% [68/82] were negative for the p16 ink4a/Ki67 dual immunostain. The 12 month follow up attrition rate was 75.6% [62/82]. The follow up Hr-HPV persistence rates in p16 ink4a/Ki67 dual positive and negative women were 72.0% [8/11] and 47.1% [24/51] respectively. These two Hr-HPV persistence rates were distinct (p=0.01). Conclusions: Approximately 20% of patients with Hr-HPV+/ NILM screening results are positive for the p16Ink4a/Ki67 dual immunostain. Hr-HPV infections in p16Ink4a/Ki67 dual immunostain positive women are more likely to persist compared to women with negative dual immunostain results. Recommendation: p16Ink4a/Ki67 dual immunostain should be done on all patients with Hr-HPV+/ NILM results to stratify them according to the risk of harboring cervical precancerous lesions.