Original ArticlesCombined Immunohistochemistry of PLK1, p21, and p53 for Predicting TP53 Status An Independent Prognostic Factor of Breast CancerWatanabe, Gou MD, PhD*; Ishida, Takanori MD, PhD*; Furuta, Akihiko MD, PhD†; Takahashi, Shin MD, PhD‡; Watanabe, Mika MD, PhD§; Nakata, Hideaki MD∥; Kato, Shunsuke MD, PhD¶; Ishioka, Chikashi MD, PhD‡; Ohuchi, Noriaki MD, PhD*Author Information *Division of surgical Oncology, Tohoku University School of Medicine ‡Department of Clinical Oncology, Research Institute of Development, Aging and Cancer, Tohoku University §Department of Pathology, Tohoku University Hospital, Sendai †Department of Breast Cancer Surgery, Ishinomaki Red Cross Hospital, Miyagi ∥Center for Kampo Medicine, Nerima General Hospital ¶Division of medical oncology, Juntendo University Hospital, Tokyo, Japan Supplemental Digital Content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website, www.ajsp.com. Conflicts of Interest and Source of Funding: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article. Correspondence: Gou Watanabe MD, PhD, Division of Surgical Oncology, Tohoku University School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8575, Japan (e-mail: firstname.lastname@example.org). The American Journal of Surgical Pathology: August 2015 - Volume 39 - Issue 8 - p 1026-1034 doi: 10.1097/PAS.0000000000000386 Buy SDC Metrics Abstract It is difficult to predict the TP53 status by p53 immunohistochemistry (IHC). We aimed to improve the accuracy of p53 IHC with p53-regulated proteins for predicting the TP53 mutation status. TP53 mutations were detected in 19 of 38 breast cancer patients (50%). Five of 7 cases of protein-truncating mutation of TP53 were completely negative for p53 IHC, whereas 11 of 12 cases of TP53 point mutation were strongly positive for p53 IHC. Therefore, to avoid false negatives, we extracted p53-dependent universally downregulated genes using microarray analysis from 38 breast cancer patients and 2 p53-inducible cell lines. From 9 commonly repressed genes, we evaluated 3 genes, baculoviral IAP repeat-containing 5 (BIRC5), polo-like kinase 1 (PLK1), and BUB1 mitotic checkpoint serine/threonine kinase (BUB1), which were previously identified as p53-dependent repressed genes. PLK1≥Allred total score (TS) 5 showed the highest correlation with TP53 mutation. To decrease false positivity, we evaluated p21 IHC. Although strong staining of p21 was observed in 4 cases (10.5%), all 4 were wild-type TP53. Thus, p53 mutation-like (p53mt-like) IHC was identified by p53 TS7,8 with PLK1≥TS 5 and p21 TS≤6. p53 mt-like IHC correlated with TP53 mutation (predictive value=0.94). In other 157 breast cancer cases, p53 mt-like was an independent prognostic marker in multivariate analysis and a strong prognostic factor. Stratification with p53 mt-like IHC identified patients with a poorer prognosis. In conclusion, we identified reliable IHC conditions to predict the TP53 status of breast cancer patients. Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.