Immunohistochemical and molecular studies on ovarian cancer progression and prognosis

Sammanfattning: Epithelial ovarian cancer (EOC) is the most lethal malignancy of the female reproductive tract. Due to vague symptomatology, the majority of EOC patients are diagnosed in advanced clinical stages with poor survival rates, despite improvements in surgical techniques and the advent of targeted therapeutics. Hence, there is an urgent need to identify novel biomarkers of early diagnosis, prognosis and treatment response. A major challenge to such efforts is the morphological and molecular heterogeneity of EOC, which should be taken into consideration in biomarker studies. The aim of this thesis was to identify novel and validate some previously investigated biomarker candidates in EOC. All studies are based on immunohistochemical (IHC) or mutation analyses of tumour samples from a pooled prospective cohort with 154 incident EOC cases from the Malmö Diet and Cancer Study and Malmö Preventive Project. Tissue microarrays (TMAs) were constructed with primary ovarian tumour samples from all cases, omental deposits from 33 cases and benign-appearing fallopian tubes from 38 cases. In addition, an independent gene expression data set with 285 EOC cases was analyzed, and relevant cell line models used for validation of investigative antibodies. In paper I, expression of the androgen receptor (AR) was demonstrated to be high in fallopian tube epithelium, and lower in invasive EOC and omental deposits. Moreover, high AR expression was an independent biomarker of favourable prognosis in the subgroup of serous carcinoma. In paper II, we used gene set enrichment analysis to compare gene expression profiles of tumours with high and low mRNA levels of a putative prognostic and treatment predictive biomarker, RNA-binding motif 3 (RBM3). Thus, several previously unknown associations of RBM3 with processes related to DNA integrity and repair were unravelled, further supporting an important role for RBM3 as a positive predictor of response to platinum-based chemotherapy. In addition, three novel biomarkers of poor prognosis in EOC were identified, i.e. Chek1, Chek2 and minichromosome maintenance complex component 3 (MCM3). Paper III provides a first description of expression of the Dachshund 2 (DACH2) protein in any form of human cancer, after its identification in the Human Protein Atlas portal. DACH2 expression was particularly high in fallopian tubes, in EOC of the serous subtype and in cisplatin-resistant cells. Moreover, DACH2 was an independent biomarker of poor prognosis in serous EOC. In paper IV, expression of the global gene regulator Special AT-rich sequence-binding protein 1 (SATB1) was found to be an independent factor of poor prognosis in high-grade EOC. In the last paper, mutation analysis of the KRAS (v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog) gene was performed in tumours from the MDCS/MPP cohort, revealing an association between KRAS mutation and good prognosis, in particular in endometroid carcinomas.