A probe selected from: A. a probe able to distinguish the presence of a particular variance or variances in the kinase domain of the erbB1 gene of a patient affected with cancer, for use in a method which predicts the likelihood of effectiveness of an EGFR tyrosine kinase inhibitor to treat cancer in a patient affected with cancer, wherein the probe is selected from nucleic acid hybridization probes, peptide nucleic acid probes, nucleotide-containing probes which also contain at least one nucleotide analog, and antibodies; or B. a probe able to distinguish the presence of a particular variance or variances in the kinase domain of the erbB1 gene of a patient affected with cancer, wherein the probe is selected from nucleic acid hybridization probes; peptide nucleic acid probes; and nucleotide-containing probes which also contain at least one nucleotide analog; or C. a probe which specifically binds under selective binding conditions to a nucleic acid sequence comprising at least one variance in the erbB1 gene, wherein the variance is a mutation in the kinase domain of erbB1 that confers a structural change in the ATP-binding pocket, and wherein the probe comprises DNA or peptide nucleic acid; or D. a nucleic acid probe which preferentially hybridizes with a nucleic acid sequence including a variance site of EGFR nucleic acid in the kinase domain of the erbB1 gene of a patient affected with cancer under selective hybridization conditions and contains complementary nucleotide bases at the variance site; wherein the variance or variances is or are selected from: a. a mutation in exon 18 that results in a substitution of cysteine for glycine at codon 719 of SEQ. ID. NO: 511 (G719C) or in a substitution of serine for glycine at codon 719 of SEQ. ID. NO: 511 (G719S); b. an in-frame deletion in exon 19 that results in a deletion of at least amino acids leucine, arginine, glutamic acid and alanine at codons 747, 748, 749, and 750 of SEQ. ID. NO: 511; or c. a mutation in exon 21 that results in an amino acid substitution of arginine for leucine at codon 858 of SEQ. ID. NO: 511 (L858R) or of glutamine for leucine at codon 861 of SEQ. ID. NO: 511 (L861Q). A. a probe able to distinguish the presence of a particular variance or variances in the kinase domain of the erbB1 gene of a patient affected with cancer, for use in a method which predicts the likelihood of effectiveness of an EGFR tyrosine kinase inhibitor to treat cancer in a patient affected with cancer, wherein the probe is selected from nucleic acid hybridization probes, peptide nucleic acid probes, nucleotide-containing probes which also contain at least one nucleotide analog, and antibodies; or B. a probe able to distinguish the presence of a particular variance or variances in the kinase domain of the erbB1 gene of a patient affected with cancer, wherein the probe is selected from nucleic acid hybridization probes; peptide nucleic acid probes; and nucleotide-containing probes which also contain at least one nucleotide analog; or C. a probe which specifically binds under selective binding conditions to a nucleic acid sequence comprising at least one variance in the erbB1 gene, wherein the variance is a mutation in the kinase domain of erbB1 that confers a structural change in the ATP-binding pocket, and wherein the probe comprises DNA or peptide nucleic acid; or D. a nucleic acid probe which preferentially hybridizes with a nucleic acid sequence including a variance site of EGFR nucleic acid in the kinase domain of the erbB1 gene of a patient affected with cancer under selective hybridization conditions and contains complementary nucleotide bases at the variance site; wherein the variance or variances is or are selected from: a. a mutation in exon 18 that results in a substitution of cysteine for glycine at codon 719 of SEQ. ID. NO: 511 (G719C) or in a substitution of serine for glycine at codon 719 of SEQ. ID. NO: 511 (G719S); b. an in-frame deletion in exon 19 that results in a deletion of at least amino acids leucine, arginine, glutamic acid and alanine at codons 747, 748, 749, and 750 of SEQ. ID. NO: 511; or c. a mutation in exon 21 that results in an amino acid substitution of arginine for leucine at codon 858 of SEQ. ID. NO: 511 (L858R) or of glutamine for leucine at codon 861 of SEQ. ID. NO: 511 (L861Q). a. a mutation in exon 18 that results in a substitution of cysteine for glycine at codon 719 of SEQ. ID. NO: 511 (G719C) or in a substitution of serine for glycine at codon 719 of SEQ. ID. NO: 511 (G719S); b. an in-frame deletion in exon 19 that results in a deletion of at least amino acids leucine, arginine, glutamic acid and alanine at codons 747, 748, 749, and 750 of SEQ. ID. NO: 511; or c. a mutation in exon 21 that results in an amino acid substitution of arginine for leucine at codon 858 of SEQ. ID. NO: 511 (L858R) or of glutamine for leucine at codon 861 of SEQ. ID. NO: 511 (L861Q).