RÉSUMÉ
KRAS mutation testing is mandatory for patients with metastatic colorectal cancer who are eligible for treatment with an epidermal growth factor receptor targeting agent, since tumors with a mutation are not sensitive to the drug. Several methods for mutation testing are in use and the need for external quality assurance has been demonstrated. An often little addressed but important issue in external quality assurance schemes is a low percentage of tumor cells in the test samples, where the analytical sensitivity of most tests becomes critical. Using artificial samples based on a mixture of cell lines with known mutation status of the KRAS gene, we assessed the reliability of a series of commonly used methods (Sanger sequencing, high resolution melting, pyrosequencing, and amplification refractory mutation system-polymerase chain reaction) on samples with 0, 2.5, 5, 10, and 15 % mutated cells. Nine laboratories throughout Europe participated and submitted a total of ten data sets. The limit of detection of each method differed, ranging from >15-5 % tumor cells. All methods showed a decreasing correct mutation call rate proportionally with decreasing percentage of tumor cells. Our findings indicate that laboratories and clinicians need to be aware of the decrease in correct mutation call rate proportionally with decreasing percentage of tumor cells and that external quality assurance schemes need to address the issue of low tumor cell percentage in the test samples.
Sujet(s)
Adénocarcinome/génétique , Tumeurs colorectales/génétique , Gènes ras , Mutation , Protéines proto-oncogènes/génétique , Assurance de la qualité des soins de santé/méthodes , Protéines G ras/génétique , Adénocarcinome/anatomopathologie , Numération cellulaire , Lignée cellulaire tumorale , Tumeurs colorectales/anatomopathologie , Analyse de mutations d'ADN/méthodes , Analyse de mutations d'ADN/normes , ADN tumoral/analyse , Humains , Limite de détection , Techniques de diagnostic moléculaire/méthodes , Techniques de diagnostic moléculaire/normes , Réaction de polymérisation en chaîne/méthodes , Réaction de polymérisation en chaîne/normes , Protéines proto-oncogènes p21(ras) , Assurance de la qualité des soins de santé/normes , Reproductibilité des résultatsRÉSUMÉ
BACKGROUND: KRAS mutation status is a candidate marker for predicting survival in patients with metastatic colorectal cancer (mCRC) treated with cetuximab (CTX). PATIENTS AND METHODS: We studied the KRAS mutation status of 113 patients with irinotecan refractory mCRC treated with CTX in clinical trials. A predictive model for objective response (OR), progression-free survival (PFS) and overall survival (OS) was constructed using logistic and Cox regression. RESULTS: OR was seen in 27 of 66 KRAS wild-type (WT) patients versus 0 of 42 in KRAS mutants. Median OS was significantly better in KRAS WT versus mutants (43.0 versus 27.3 weeks; P = 0.020). Decrease in tumor sizes was significantly larger at all time points in WT patients. KRAS WT patients with an initial relative decrease of tumor size >9.66% at week 6 had a significantly better median OS compared with all other patients (74.9 versus 30.6 weeks; P = 0.0000025). Within KRAS WT patients OS was significantly better in patients with an initial decrease compared with those without [median OS: 74.9 versus 30.6 weeks (P = 0.00000012)]. CONCLUSIONS: KRAS WT status is associated to survival benefit in CTX treated mCRC. This benefit is even more pronounced in those patients with early radiological response. These characteristics may be exploited for response prediction.
