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P. Kuo

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    MO03 - Thymic Malignancies (ID 123)

    • Event: WCLC 2013
    • Type: Mini Oral Abstract Session
    • Track: Medical Oncology
    • Presentations: 1
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      MO03.08 - Increased Galectin-1 Expression in a Thymic Epithelial Tumor Tissue Microarray (TMA) and Galectin-1 Knockdown Studies in a Thymoma Cell Line (ID 1238)

      10:30 - 12:00  |  Author(s): P. Kuo

      • Abstract
      • Presentation
      • Slides

      Thymoma is a rare malignancy with a paucity of data on biology. Thymic epithelial tumors are often admixed with developing T-lymphocytes in the microenvironment. Galectin-1 (gal-1) is a beta-galactosidase binding protein involved in T-cell development via thymic stromal and thymocyte interaction as well as thymocyte development through negative selection. Gal-1 also induces apoptosis of effector T-lymphocytes, promotes angiogenesis, and is a poor prognostic indicator when overexpressed in several tumor types. To our knowledge expression of gal-1 has not been examined in thymic epithelial tumors.

      A TMA was constructed from 68 patients with thymic malignancies and 8 benign thymic controls at Stanford University School of Medicine (Stanford, CA). Immunohistochemical stains for galectin-1 (1:200 dilution; citrate pre-treatment; mouse monoclonal; Novocastra) were performed on 4 µM-thick TMA sections. Galectin-1 cytoplasmic staining of the epithelial cell component was scored as negative (0), focal positive (1+), or strong positive (2+) by a Stanford pathologist, who was blinded to the clinical data. Gal-1 expression was averaged for each patient sample. Statistical analysis was performed using SAS Enterprise Guide v5.0 (Cary, NC). Non-parametric statistical analyses were used to compare average patient gal-1 expression between thymic tumors and benign thymic controls. Stable gal-1 knockdown was achieved in IU-TAB1, a human thymoma WHO type AB cell line, using the pLKo.1 vector with gal-1 shRNA (Open Biosystems). Lentivirus was produced using the Trans-Lentiviral Packaging System (Thermo Scientific). In vitro proliferation cell counts were performed by hemocytometer. After hypoxia exposure (0.5% O~2~), apoptotic cells were labeled using the APO-Direct kit and quantified by flow cytometry (BD Biosciences).

      Demographics for 68 patients: M:F (53%/47%), Mean age at diagnosis: 55 years, WHO Histology: A (10%), B (57%), AB (24%), C (4%), unclassified (4%), Pathologic Maseoka Stage: I (46%), IIa (18%), IIb (4%), III (18%), IVa (9%) IVb (6%). Gal-1 expression was increased among thymic tumor tissue compared to unpaired controls (mean avg gal-1 expression 1.5 vs. 0.125, p=0.0012, Kruskal-Wallis test). Logistic regression of tumor vs. control thymus by gal-1 generated a C-statistic of 0.845. A significant increase in gal-1 expression was noted across all WHO thymoma subtypes except thymic carcinoma (type C) (p < 0.05, non-parametric ANOVA with post-hoc ranked Dunnett’s t-test). Among 11 thymic tumors analyzed with paired adjacent resected benign thymus tissue from the same patient, a significant increase was noted in gal-1 expression among tumor compared with adjacent resected normal benign thymus (mean avg gal-1 1.82 vs. 0.35, p=0.004, sign-rank test). In vitro, gal-1 knockdown did not affect IU-TAB1 proliferation. Preliminary results showed gal-1 knockdown increased apoptosis under hypoxia compared to scramble control.

      Gal1 expression was increased among thymoma compared with benign thymus controls and paired adjacent resected benign thymus. A robust C-statistic of 0.845 indicates that gal-1 expression may discriminate tumor from benign thymus. Increased gal-1 expression was conserved across WHO histologic subtype except for thymic carcinoma—whose analysis was limited due to small sample size. Gal-1 knockdown might increase apoptosis under hypoxia. We are continuing to investigate the biologic and clinical significance of increased gal-1 expression in thymoma.

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