Method to determine responsiveness of cancer to epidermal growth factor receptor targeting treatments

A method for determining an increased likelihood of pharmacological effectiveness of treatment by gefitinib or erlotinib in an individual diagnosed with non-small cell lung cancer comprising:

• obtaining DNA from a non-small cell lung cancer tumor sample from the individual;
• and determining the presence or absence of at least one nucleotide variance in exon 18, 19, or 21 of the epidermal growth factor receptor (EGFR) gene in the DNA, wherein the presence of at least one nucleotide variance selected from:
• 1) an in-frame deletion in exon 19 of the EGFR gene consisting of a deletion within codons 746 to 753 that results in amino acid changes comprising a deletion of at least amino acids leucine, arginine, and glutamic acid at position 747, 748, and 749 of SEQ ID NO:512;
• 2) a substitution in exon 21 that results in an amino acid change consisting of a substitution of arginine for leucine at position 858 (L858R) of SEQ ID NO:512, or a substitution in exon 21 that results in an amino acid change consisting of a substitution of glutamine for leucine at position 861 (L861Q) of SEQ ID NO:512;
• or
• 3) a substitution in exon 18 that results in an amino acid change consisting of a substitution of cysteine for glycine at position 719 (G719C) of SEQ ID NO:512
• indicates an increased likelihood of pharmacological effectiveness of treatment by gefitinib or erlotinib in the individual.