Method and compositions for screening for the presence of Epidermal Growth Factor Receptor variant 3 (EGFR(v3)) in a sample are described. The method comprises obtaining a sample containing a plurality of cells; hybridizing a set of chromosomal probes to the sample, wherein the set comprises an EGFR(v3)-probe and a probe to chromosome 7 different from an EGFR(v3)-probe; and visualizing the hybridization pattern of the set of chromosomal probes in the plurality of cells of the sample, wherein the presence of at least one copy of chromosome 7 lacking a hybridization signal of the EGFR(v3)-probe in at least one cell is indicative of the presence of the EGFR(v3) in the sample. The method and compositions are suitable for diagnosing the therapeutic outcome for treating a patient having a cancer with an anti-EGFR therapeutic agent and for screening a sample for a predisposition for forming an EGFR-associated cancer.