Low Incidence along with Low mRNA Levels of EGFRvIII in Prostate and Colorectal Cancers Compared to Glioblastoma

Background: The presence as well as the potential role of EGFR vIII in tumors other than glioblastoma still remains a controversial subject with many contradictory data published. Previous analyses, however, did not consider the level of EGFR vIII mRNA expression in different tumor types. Methods: Appropriately designed protocol for Real-time quantitative reverse-transcription PCR (Real-time qRT-PCR) was applied to analyze EGFR vIII and EGFR WT mRNA expression in 155 tumor specimens. Additionally, Western Blot (WB) analysis was performed for selected samples. Stable cell lines showing EGFR vIII expression (CAS-1 and DK-MG) were analyzed by means of WB, immunocytochemistry (ICC) and fluorescence in situ hybridization (FISH). Results: Our analyses revealed EGFR vIII expression in 27.59% of glioblastomas (8/29), 8.11% of colorectal cancers (3/37), 6.52% of prostate cancers (3/46) and none of breast cancers (0/43). Despite the average relative expression of EGFR vIII varying greatly among tumors of different tissues (approximately 800-fold) or even within the same tissue group (up to 8000-fold for GB), even the marginal expression of EGFR vIII mRNA can be detrimental to cancer progression, as determined by the analysis of stable cell lines endogenously expressing the oncogene. Conclusion: EGFR vIII plays an unquestionable role in glioblastomas with high expression of this oncogene. Our data suggests that EGFR vIII importance should not be underestimated even in tumors with relatively low expression of this oncogene.