p16 overexpression and 9p21 deletion are linked to unfavorable tumor phenotype in breast cancer

// Patrick Lebok 1, * , Magdalena Roming 1, * , Martina Kluth 1 , Christina Koop 1 , Cansu Özden 1 , Berivan Taskin 1 , Khakan Hussein 1 , Annette Lebeau 1 , Isabell Witzel 2 , Linn Wölber 2 , Stefan Geist 3 , Peter Paluchowski 3 , Christian Wilke 4 , Uwe Heilenkötter 5 , Volkmar Müller 2 , Barbara Schmalfeldt 2 , Ronald Simon 1 , Guido Sauter 1 , Luigi Terracciano 6 , Rainer Horst Krech 7 , Albert von der Assen 8 , Eike Burandt 1 1 Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany 2 Department of Gynecology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany 3 Department of Gynecology, Regio Clinic Pinneberg, Pinneberg, Germany 4 Department of Gynecology, Regio Clinic Elmshorn, Elmshorn, Germany 5 Department of Gynecology, Clinical Centre Itzehoe, Itzehoe, Germany 6 Department of Pathology, Basel University Clinics, Basel, Switzerland 7 Institute of Pathology, Clinical Centre Osnabrück, Osnabrück, Germany 8 Breast Centre Osnabrück, Osnabrück, Germany * These authors contributed equally to this work Correspondence to: Partick Lebok, email: p.lebok@uke.de Keywords: breast cancer, 9p21 deletion, TMA, p16 expression, CDKN2A Received: May 04, 2016 Accepted: November 01, 2016 Published: November 09, 2016 ABSTRACT Overexpression of the p16 tumor suppressor, but also deletion of its gene locus 9p21, is linked to unfavorable tumor phenotype and poor prognosis in breast cancer. To better understand these contradictory observations, and to clarify the prognostic impact of p16 expression and 9p21 deletion, a tissue microarray (TMA) with 2,197 breast cancers was analyzed by fluorescence in-situ hybridization and immunohistochemistry (FISH) for 9p21 deletion and p16 expression. p16 immunostaining was weak in 25.6%, moderate in 7.1%, and strong in 12.7% of 1,684 evaluable cancers. Strong p16 staining was linked to advanced tumor stage ( p = 0.0003), high-grade ( p < 0.0001), high tumor cell proliferation ( p < 0.0001), negative hormone receptor (ER/PR) status ( p < 0.0001 each), and shorter overall survival ( p = 0.0038). 9p21 deletion was found in 15.3% of 1,089 analyzable breast cancers, including 1.7% homozygous and 13.6% heterozygous deletions. 9p21 deletion was linked to adverse tumor features, including high-grade ( p < 0.0001) and nodal positive cancers ( p = 0.0063), high cell proliferation ( p < 0.0001), negative hormone receptor (ER/PR) status ( p ≤ 0.0006), and HER2 amplification ( p = 0.0078). Patient outcome was worse in 9p21 deleted than in undeleted cancers ( p = 0.0720). p16 expression was absent in cancers harboring homozygous 9p21 deletions, but no difference in p16 expression was found between cancers with (59.2% p16 positive) and without heterozygous 9p21 deletion (51.3% p16 positive, p = 0.0256). In summary, p16 expression is unrelated to partial 9p21 deletion, but both alterations are linked to aggressive breast cancer phenotype. High-level p16 expression is a strong predictor of unfavorable disease course in breast cancer.