Expression Is a Marker of Unfavorable Prognosis in Ovarian Carcinoma of Clear Cell Subtype

IGF2BP3 (IMP3) expression is a marker of unfavorable prognosis in ovarian carcinoma of clear cell subtype

Martin Ko¨bel1,2, Haodong Xu3, Patricia A Bourne3, Betsy O Spaulding4, Ie-Ming Shih5, Tsui-Lien Mao6, Robert A Soslow7, Carol A Ewanowich8, Steve E Kalloger1, Erika Mehl1, Cheng-Han Lee1, David Huntsman1 and C Blake Gilks1

1Department of Pathology, Genetic Pathology Evaluation Centre of the Prostate Research Centre, Vancouver General Hospital and British Columbia Cancer Agency, Vancouver, BC, Canada; 2Institute of Pathology, Charite´ Hospital, Berlin, Germany; 3Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY, USA; 4Dako North America, Carpinteria, CA, USA; 5Department of Pathology, Johns Hopkins University, Baltimore, MD, USA; 6Department of Pathology, National Taiwan University Hospital, Tapei, Taiwan; 7Surgical Pathology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA and 8Department of Laboratory Medicine and Pathology, University of Alberta and Royal Alexandra Hospital, Edmonton, AB, Canada

Clear cell carcinoma is an uncommon subtype of ovarian carcinoma, accounting for 10% of cases. Clear cell carcinoma typically presents with stage I or II disease, and in this setting prognostic markers could aid in management decisions, in particular the decision to treat with adjuvant chemotherapy. We tested whether expression of insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3, also known as IMP3) can serve as a new biomarker to predict outcome for patients with clear cell carcinoma and other subtypes of ovarian carcinoma. The expression of IGF2BP3 was evaluated by immunohistochemistry in 475 ovarian carcinomas of different subtypes and correlated with disease-specific survival. IGF2BP3 antibody specificity was validated by correlation of IGF2BP3 protein with mRNA expression level in a series of 35 ovarian carcinomas (r ¼ 0.849, Po0.0001). IGF2BP3 protein expression was an independent marker of reduced disease-specific survival (risk ratio 2.9, 95% confidence interval 1.4–5.8) in the clear cell subtype (N ¼ 128), but not in high-grade serous (N ¼ 198) or endometrioid (N ¼ 121) carcinomas. The prognostic significance of IGF2BP3 expression for reduced disease-specific survival (risk ratio 2.6, 95% confidence interval 1.3–5.0) was confirmed in an independent series of cases (N ¼ 150) from three different centers in North America. We conclude that IGF2BP3 is the first biomarker of prognostic significance in ovarian clear cell carcinoma that has been validated in an independent case series. Modern Pathology (2009) 22, 469–475; doi:10.1038/modpathol.2008.206; published online 9 January 2009

Keywords: ovarian clear cell carcinoma; IGF2BP3; IMP3; prognosis; immunohistochemistry; cancer

The insulin-like growth factor mRNA-binding pro- little or no detectable protein in normal adult tein family comprises three proteins (IGF2BP1–3), tissues.5 We have recently shown that IGF2BP1 which regulate mRNA transport, translation, and (alias IMP1) is overexpressed in high-grade ovarian turnover by binding the coding regions of target carcinomas of serous and clear cell subtypes.6 mRNAs such as IGF2 (insulin-like growth factor 2), Another family member, IGF2BP3, was cloned from MYC, and ACTB (b-actin).1–4 IGF2BP expression is a pancreatic tumor cDNA screen and was originally almost exclusively restricted to embryogenesis, with designated as KOC (KH-domain-containing protein overexpressed in cancer).7 IGF2BP3 expression has been associated with an unfavorable outcome in Correspondence: Professor CB Gilks, MD, Department of Pathol- renal clear cell carcinoma.8,9 On the basis of this ogy, Vancouver General Hospital, Room 1207 1st floor JPPN, finding, we postulated that IGF2BP3 expression 855 West 12th Ave, Vancouver, BC, C