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High WT1 Expression Is Associated with Very Poor Survival of Patients with Osteogenic Sarcoma Metastasis

Authors' Affiliations: ¹ Department of Orthopedics, Mayo Clinic and Foundation, Rochester, Minnesota and ² Department of Orthopedic Surgery, Johns Hopkins School of Medicine, Baltimore, Maryland

Requests for reprints: Gobinda Sarkar, Department of Orthopedics, Mayo Clinic, 3-93 Medical Science Building, 200 1st Street, Southwest, Rochester, MN 55905. Phone: 507-284-5293; Fax: 507-284-5075; E-mail: sarkar.gobinda{at}mayo.edu.

Purpose: Although metastasis is the primary determinant of poor survival of patients with osteogenic sarcoma, some patients live much longer than others, indicating metastatic heterogeneity underlying survival outcome. The purpose of the investigation was to identify genes underlying survival outcome of patients with osteogenic sarcoma metastasis.

Experimental Design: We have used microarray to first compare mRNA expression between normal bone and osteogenic sarcoma specimens, identified genes overexpressed in osteogenic sarcoma, and compared expression of the selected gene between a poorly metastatic (SAOS) and two highly metastatic cell lines (LM8 and 143B). Finally, expression of the selected gene was assessed by immunostaining of osteogenic sarcoma samples with known survival outcome.

Results: Microarray analysis revealed 5.3-fold more expression of WT1 mRNA in osteogenic sarcoma compared with normal bone and >2-fold overexpression in 143B and LM8 cells compared with SAOS. Furthermore, WT1 mRNA was absent in normal bone (10 of 10) by reverse transcription-PCR but present in osteogenic sarcoma–derived cell lines (5 of 8). One hundred percent (42 of 42) of low-grade osteogenic sarcoma specimens expressed no WT1 as determined by immunostaining; however, 24% (12 of 49) of the high-grade specimens showed intense staining. Mean survival of patients with high-grade metastatic osteogenic sarcoma but low WT1 staining (27 of 37) was 96.5 ± 129.3 months, whereas mean survival of patients with high-grade metastatic osteogenic sarcoma having intense staining (10 of 37) was 18.3 ± 12.3 months (P > 0.0143). All splice variants of WT1 mRNA, including a hitherto unknown variant (lacking exons 4 and 5), were found to be expressed in osteogenic sarcoma.

Conclusion: WT1 seems to be associated with very poor survival of patients with osteogenic sarcoma metastasis.