PIK3CA novel mutations detection for diagnosis of acquired cetuximab resistance in metastatic colorectal cancer patients

A method for diagnosing or assisting in diagnosing of acquired cetuximab resistance in metastatic colorectal cancer in a subject, the method comprising administering a substance used for detecting whether Exon 19 in the PIK3CA gene of the subject has a gene mutation, wherein the substance used for detecting whether Exon 19 in the PIK3CA gene has a gene mutation is Primer Pair 1 and/or Primer Pair 2, wherein Primer Pair 1 is a primer pair composed of two single stranded DNA molecules shown by SEQ ID NO:

• 2 and SEQ ID NO:
• 3, and wherein Primer Pair 2 is a primer pair composed of two single stranded DNA molecules shown by SEQ ID NO:
• 4 and SEQ ID NO:
• 5;
• detecting whether the subject has at least one of following (a)-(e) mutations:
• (a) Lysine at the 944th amino acid of the PIK3CA gene coding protein mutates into Asparagine;
• (b) Phenylalanine at the 930th amino acid of the PIK3CA gene coding protein mutates into Serine;
• (c) Valine at the 955th amino acid of the PIK3CA gene coding protein mutates into Isoleucine;
• (d) Valine at the 955th amino acid of the PIK3CA gene coding protein mutates into Glycine;
• and
• (e) Lysine at the 966th amino acid of the PIK3CA gene coding protein mutates into Glutamic Acid;
• and
• determining that the subject will develop drug resistance or will be a candidate that develops drug resistance when receiving or continuing to receive cetuximab for treating metastatic colorectal cancer, if the subject has at least one of the above (a)-(e) mutations.