Abstract A11: Loss of LKB1 is an early event in high-grade serous carcinoma

Background : LKB1 is a ubiquitously expressed serine/threonine protein kinase recently ranked sixteenth on the list of top cancer genes. Inactivating germ-line mutations in LKB1 gene on chromosome 19p13.3 found in 60–70% of patients with Peutz-Jeghers syndrome (PJS), leading to increased risk of developing cancers of epithelial origin. Loss of LKB1 protein with underlying LKB1 gene methylation previously found in high-grade breast carcinoma – low expression associated with shorter relapse-free survival. Heterozygous mutations of LKB1 and p53 genes cooperate in the acceleration of tumorigenesis in mice. High-grade serous ovarian cancer (HGSC) is rarely diagnosed at an early and potentially curable stage, effective early detection and preventative strategies are few. In a previously published microarray study, we observed that LKB1 mRNA was significantly lower in Fallopian tube cancers and HGSC. Recently the discovery of occult invasive and intraepithelial tubal carcinomas in BRCA1 mutation carriers, who are at high risk of serous cancer, undergoing prophylactic surgery has focused attention on the fallopian tube epithelium as the cell of origin and has led to the reporting of putative serous cancer precursor lesions. We therefore, sought to determine the expression of LKB1 in different histological subtypes of ovarian cancer and in early lesions; and the effect of loss of LKB1 on fallopian tube epithelial cells in vitro. Methodology : Archived sections of ovarian tumors were reviewed, paraffin blocks selected, and tissue microarrays created using triplicate 0.6 mm cores. The major histological types included were: high grade serous (n=201), non-serous (n=87), and low grade (micropapillary) (n=12) carcinomas, serous tumors of low malignant potential (n=26) and STICS (n=15). Immunohistochemistry for LKB1 protein (Santa Cruz mouse mAb sc-32245) was performed using standard techniques. Percentage of tumor cells with positive cytoplasmic staining (0–3), staining intensity (0–3) and histoscores were determined by viewing digitalized images with Aperio ImageScope software. A combined score of > 4 was considered positive. Fishers exact test with 95% confidence intervals was used to determine the significance of results. Fallopian tube epithelial cells were established from freshly digested tissue and infected with shRNA targeting LKB1. In vitro assays to determine proliferation and malignant transformation were used. Results : Loss of cytoplasmic LKB1 protein expression is more frequently observed in sporadic and hereditary high-grade serous carcinomas compared to other histological types, including low-grade serous carcinoma and serous tumors of low malignant potential. LKB1 may be exclusively involved in the high-grade serous oncogenic pathway and not in the development of low-grade serous carcinoma. Loss of LKB1 in early lesions was observed in 15/15 cases and indicates a role for in sporadic HGSC tumorigenesis in corporation with previously identified oncogenes. The frequency of LKB1 loss in high-grade tumors (67–69%) is similar to frequency of p53 mutations previously observed (70%). Citation Information: Cancer Prev Res 2011;4(10 Suppl):A11.