PIK3CA Mutation is Strongly Associated with K-ras 12/13 Mutation in Stage II/III Colorectal Cancer
Session type: Poster / e-Poster / Silent Theatre session
Ras and Raf mutations in colorectal cancer are associated with poorer outcome and lack of response to anti-EGFR antibodies. The importance of PIK3CA mutations has not been as extensively investigated. In this study the relationship between PIK3CA, mutations in K-ras, N-ras, B-raf and a number of other clinicopathological features have been examined in Quasar-I, a large phase III adjuvant chemotherapy clinical trial.
PIK3CA mutation status was investigated in a test set of 900 cases. Tumour DNA was extracted from a formalin-fixed paraffin-embedded block in each case. We have assessed PIK3CA mutations in exon 9 (codons 542/545/546) and exon 20 (codon 1047) by pyrosequencing.
Summary of results: Data was available in 873 cases. The mutation rate was 13.9 %. 83 cases had a mutation in exon 9 and 38 cases had a mutation in exon 20. There were no double PIK3CA mutations. 76 (62.8% of all PIK3CA mutated cases) had a K-ras12/13 and a PIK3CA mutation (P ≤ 0.0001). There was no association between PIK3CA mutation and sex, site, stage, tumour content, stromal content, K-ras 61, K-ras 146, N-ras 12/13, N-ras 61 or B-raf V600E mutations.
PIK3CA mutations are associated with K-ras mutations and this should be considered when ascribing a poor outcome to PIK3CA mutations.