Comparing the scoring mechanisms of p16INK4a immunohistochemistry based on independent nucleic stains and independent cytoplasmic stains in distinguishing between endocervical and endometrial adenocarcinomas in a tissue microarray study

Endocervical adenocarcinomas (ECAs) and endometrial adenocarcinomas (EMAs) are malignancies that affect the uterus; however, their biological behaviors are quite different. This distinction has clinical significance because the appropriate therapy may depend on the site of tumor origin. The purpose of this study is to evaluate two different scoring mechanisms of p16INK4a immunohistochemical (IHC) stain in distinguishing between primary ECAs and EMAs. A tissue microarray (TMA) was constructed using formalin-fixed, paraffin-embedded tissue from hysterectomy specimens, including 14 ECAs and 21 EMAs. Tissue array sections were stained with a commercially available antibody, p16INK4a. The avidin–biotin complex method was used to visualize antigens. The staining intensity and extent of the IHC reactions were evaluated using a semi-quantitative scoring system. Two scoring methods were defined on the following bases: (1) independent cytoplasmic staining alone, irrespective of nucleic stain (Method C) and (2) independent nucleic staining alone, irrespective of cytoplasmic staining. (Method N). Of the two scoring mechanisms for p16INK4a expression, Method N showed a significant difference (P = 0.015), but Method C showed no significant (P = 0.432) frequency differences in distinguishing between ECAs and EMAs. However, Method N had a higher overall accuracy rate (71.4%) in accurately diagnosing ECAs from EMAs in the total number of p16INK4a IHC cases. According to the data of p16INK4a expression in this TMA study, Method N is favorable and efficient in distinguishing between ECAs and EMAs, while Method C is not.