Abstract 2217: Primary tumor loss of heterozygosity proximal to M6P/IGF2R locus is predictive for the presence and persistence of disseminated tumor cells in the bone marrow of ovarian cancer patients
Authors: Kuhlmann Jan D. , Schwarzenbach Heidi , Otterbach Friedrich , Heubner Martin , Wimberger Pauline , Worm Karl H. , Kimmig Rainer , Kasimir-Bauer Sabine 
Published: June 2012

Introduction: Disseminated tumor cells (DTC) in the bone marrow (BM) are present in about 35% of all ovarian cancer patients before surgery and after platinum-based chemotherapy which has been associated with an adverse prognosis. Since invasive BM aspirations are less accepted and often not feasible, it would be highly desirable to unmask a molecular biomarker in the primary tumor predicting tumor cell spread and persistence. It was the purpose of the study to 1) investigate loss of heterozygosity (LOH) incidence at four ovarian cancer relevant chromosomal loci involved in inter alia apoptosis, platinum sensitivity or DNA repair in primary ovarian tumor tissue 2) assess the prognostic value of LOH after a median follow-up time of three years and 3) correlate LOH incidence with the occurrence of DTC before surgery and after platinum-based chemotherapy.

Methods: In total, 88 ovarian cancer patients were recruited for this study. Primary tumor DNA was extracted from paraffin embedded tissue and analyzed for LOH status at four polymorphic microsatellite markers including D10S1765 (PTEN locus), D13S218 (BRCA1 locus), D17S855 (BRCA2 locus) and D6S1581 (proximal to M6P/IGF2R locus) using PCR-based fluorescence microsatellite analysis. BM aspirates were feasible in 53 patients before surgery and in 40 patients after chemotherapy. BM cells were isolated from heparinized BM by Ficoll-Hypaque density gradient centrifugation and analyzed for DTC by immunocytochemistry using the pan-cytokeratin antibody A45-B/B3.

Results: In our cohort of 88 patients, we recorded at least one LOH in 56/88 patients (63%), two LOH in 30/88 patients (34%), three LOH in 8/88 patients (9%) and LOH at all four markers in 3/88 patients (3%), respectively. The occurrence of LOH at the entire marker set significantly correlated with tumor grading (p=0.0001) and histology (p=0.004). The frequency of LOH at the marker D10S1765 correlated with FIGO stage (p=0.046) and grading (p=0.05) whereas LOH at D17S855 was associated with grading (p=0.023) and histology (p=0.012). The occurrence did not correlate with disease free as well as overall survival. Prior to surgery, DTC were detected in 26/53 patients (49%) with a median number of 6 cells (range 1-38 cells). After chemotherapy, 20/40 patients (50 %) revealed DTC in their BM with a median number of 10 cells, ranging from 1 to 35 cells. Interestingly, the LOH incidence proximal to D6S1581 significantly correlated with DTC presence before surgery (p=0.05) as well as DTC persistence after chemotherapy (p=0.022).

Conclusion: In primary ovarian tumors, allelic loss proximal to D6S1581 might serve as a potential molecular biomarker for the presence and persistence of DTC in the BM. Further investigations have to prove whether such a molecular marker could replace invasive BM aspirations in the future.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2217. doi:10.1158/1538-7445.AM2011-2217