Breast cancer is the most commonly diagnosed cancer among women in both developed and developing countries. Studies have shown several risk factors including viral agents especially high risk HPV which can be diagnosed by studying p16 INK4A expression on formalin fixed, paraffin wax embedded tissue blocks. p16Immunohistochemistry is considered the best candidate for initial diagnosis of high risk HPV related lesions because of its availability, easy interpretation and its high sensitivity and specificity. This study examined p16 INK4A expression in series of invasive breast carcinoma at Kenyatta National Hospital in order to determine its utility in identifying high risk HPV related invasive breast carcinomas. Objectives The primary objective was to establish the p16 INK4A expression as a marker of high risk HPV infection in women invasive breast carcinomas at Kenyatta National Hospital. Design: Our study was retrospective laboratory based. ixSetting: The study was conducted at University of Nairobi, anatomic pathology laboratory at Kenyatta National Hospital. Study population: Ninety-six (96) formalin fixed, paraffin wax embedded tissue blocks from breast biopsies reported as invasive breast carcinomas in women who attended KNH from January 2013 to February 2016. Results: Our study demonstrated that 25 years old patient was the youngest while the oldest patient was 96 years old. The mean age was 46 years. The most affected age group was 41-50 age group (37.5%) followed by 31-40 age group (27%). The predominant histological type was invasive ductal carcinoma NOS (82.2%). Invasive breast carcinoma grade II were predominant (47.3 %) and majority of the patients presented with stage III invasive breast carcinomas (65.6 %). Positivity was considered when there is nuclear and cytoplasmic staining or expression for p16INK4A. Positivity was noted in 11.4% of our cases and majority of the positive cases were noted among grade III breast carcinoma cases. There was no statistically significant association between invasive breast carcinoma stage or grade to p16INK4A expression. Conclusion: High risk HPV infection has been identified in a series of high grade and advanced stageinvasive breast carcinomas in Kenyatta National Hospital. Women aged from 40-50 years are the most affected by invasive breast carcinoma. Mastectomy was most common specimen. P16INK4A expression is not associated with breast tumor stage or grade

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