Nucleophosmin expression in ovarian cancer.

Abstract

e15582 Background: The nucleolar protein, nucleophosmin (NPM1) is implicated multiple cellular processes, including proliferation, duplication of centrosomes, ARF-HDM2-p53 signaling. NPM1 is associated with sites of double strand DNA breaks, with persistence of its expression indicative of impaired DNA repair. Data from the TCGA data have emphasized that genomic instability through impaired DNA repair processes is a characteristic feature of many ovarian cancers. Our aim was to determine the expression of NPM1 in ovarian cancers and to determine the relationship between NPM1 expression and clinical outcomes including overall survival (OS), progression-free survival (PFS) and chemotherapy response. Methods: Tissue microarrays were created from 209 patients treated for ovarian cancer at a single institution from 1994-2004. Expression levels of NPM1 were examined by immunohistochemical staining. Slides were scored using the an automated image capture and analysis system. Positive nuclear staining was used to stratify tumors into high (>50%) and low (<50%) groups, and the results were related to overall survival (OS) and progression-free survival (PFS) via Kaplan-Meier analysis. The relationship between ki67, a proliferation marker and pH2AX, a mark of double strand DNA breaks was measured with Spearman rank correlation coefficient analyses. Results: The majority of tumors, 140/209 (69%) were of serous histology, advanced stage 146/209 (70%) and high grade 158/209 (76%). There was >50% NPM1 expression in 83/209 (40%) and <50% in 126/209 (60%) of the cases. Expression of NPM1 was higher in high grade tumors, and its expression alone was a significant predictor of PFS (p=0.022) but not OS (p=0.053). When adjusting for other predictors, NPM1 expression was predictive of PFS (p=0.047), but not OS (p=0.054). No relationship between NPM1 expression and response to platinum chemotherapy was observed. However, NPM1 expression correlated with Ki67 (r=0.43, p<0.0001) and pH2AX (r=0.22, p=0.0014). Conclusions: NPM1 expression is a mark of poor prognosis in ovarian cancer. Whether these observations reflect increased proliferation and/or genomic instability in ovarian cancer cells will be the focus of future investigation.