Expression and amplification of therapeutic target genes in retinoblastoma

Purpose: We set out to evaluate alterations of the therapeutic target genes KIT (CD 117), EGFR, and HER-2 in human retinoblastoma. Methods: Ninety-five formalin-fixed, paraffin-embedded retinoblastomas were brought into a tissue microarray (TMA) format. Immunohistochemistry was performed to analyze the expression of CD117, EGFR, and HER-2. Fluorescence in situ hybridization (FISH) was utilized for detection of EGFR amplifications. Three tumors with strong CD117 positivity were sequenced for KIT exon 11 mutations. Results: Detectable CD117 expression was seen in 19% of all interpretable cases. Sequence analysis of the three tumors with the strongest CD117 expression revealed no mutations. EGFR was positive in 14% of all cases. No EGFR amplification was observed by FISH, however. All tumors were negative for HER-2 expression. Conclusions: Our data suggest that selected cases of retinoblastoma may be candidates for anti-EGFR and imatinib mesylate (STI571) therapy.