Effects of KRAS, BRAF, NRAS, and PIK3CA mutations on the efficacy of cetuximab plus chemotherapy in chemotherapy-refractory metastatic colorectal cancer: a retrospective consortium analysis.
BACKGROUND
Following the discovery that mutant KRAS is associated with resistance to anti-epidermal growth factor receptor (EGFR) antibodies, the tumours of patients with metastatic colorectal cancer are now profiled for seven KRAS mutations before receiving cetuximab or panitumumab. However, most patients with KRAS wild-type tumours still do not respond. We studied the effect of other downstream mutations on the efficacy of cetuximab in, to our knowledge, the largest cohort to date of patients with chemotherapy-refractory metastatic colorectal cancer treated with cetuximab plus chemotherapy in the pre-KRAS selection era.


METHODS
1022 tumour DNA samples (73 from fresh-frozen and 949 from formalin-fixed, paraffin-embedded tissue) from patients treated with cetuximab between 2001 and 2008 were gathered from 11 centres in seven European countries. 773 primary tumour samples had sufficient quality DNA and were included in mutation frequency analyses; mass spectrometry genotyping of tumour samples for KRAS, BRAF, NRAS, and PIK3CA was done centrally. We analysed objective response, progression-free survival (PFS), and overall survival in molecularly defined subgroups of the 649 chemotherapy-refractory patients treated with cetuximab plus chemotherapy.


RESULTS
40.0% (299/747) of the tumours harboured a KRAS mutation, 14.5% (108/743) harboured a PIK3CA mutation (of which 68.5% [74/108] were located in exon 9 and 20.4% [22/108] in exon 20), 4.7% (36/761) harboured a BRAF mutation, and 2.6% (17/644) harboured an NRAS mutation. KRAS mutants did not derive benefit compared with wild types, with a response rate of 6.7% (17/253) versus 35.8% (126/352; odds ratio [OR] 0.13, 95% CI 0.07-0.22; p<0.0001), a median PFS of 12 weeks versus 24 weeks (hazard ratio [HR] 1.98, 1.66-2.36; p<0.0001), and a median overall survival of 32 weeks versus 50 weeks (1.75, 1.47-2.09; p<0.0001). In KRAS wild types, carriers of BRAF and NRAS mutations had a significantly lower response rate than did BRAF and NRAS wild types, with a response rate of 8.3% (2/24) in carriers of BRAF mutations versus 38.0% in BRAF wild types (124/326; OR 0.15, 95% CI 0.02-0.51; p=0.0012); and 7.7% (1/13) in carriers of NRAS mutations versus 38.1% in NRAS wild types (110/289; OR 0.14, 0.007-0.70; p=0.013). PIK3CA exon 9 mutations had no effect, whereas exon 20 mutations were associated with a worse outcome compared with wild types, with a response rate of 0.0% (0/9) versus 36.8% (121/329; OR 0.00, 0.00-0.89; p=0.029), a median PFS of 11.5 weeks versus 24 weeks (HR 2.52, 1.33-4.78; p=0.013), and a median overall survival of 34 weeks versus 51 weeks (3.29, 1.60-6.74; p=0.0057). Multivariate analysis and conditional inference trees confirmed that, if KRAS is not mutated, assessing BRAF, NRAS, and PIK3CA exon 20 mutations (in that order) gives additional information about outcome. Objective response rates in our series were 24.4% in the unselected population, 36.3% in the KRAS wild-type selected population, and 41.2% in the KRAS, BRAF, NRAS, and PIK3CA exon 20 wild-type population.


CONCLUSIONS
While confirming the negative effect of KRAS mutations on outcome after cetuximab, we show that BRAF, NRAS, and PIK3CA exon 20 mutations are significantly associated with a low response rate. Objective response rates could be improved by additional genotyping of BRAF, NRAS, and PIK3CA exon 20 mutations in a KRAS wild-type population.


BACKGROUND
Belgian Federation against Cancer (Stichting tegen Kanker).
De Roock
Wendy
W
Centre for Human Genetics, KU Leuven, Leuven, Belgium.
Claes
Bart
B
Bernasconi
David
D
De Schutter
Jef
J
Biesmans
Bart
B
Fountzilas
George
G
Kalogeras
Konstantine T
KT
Kotoula
Vassiliki
V
Papamichael
Demetris
D
Laurent-Puig
Pierre
P
Penault-Llorca
Frédérique
F
Rougier
Philippe
P
Vincenzi
Bruno
B
Santini
Daniele
D
Tonini
Giuseppe
G
Cappuzzo
Federico
F
Frattini
Milo
M
Molinari
Francesca
F
Saletti
Piercarlo
P
De Dosso
Sara
S
Martini
Miriam
M
Bardelli
Alberto
A
Siena
Salvatore
S
Sartore-Bianchi
Andrea
A
Tabernero
Josep
J
Macarulla
Teresa
T
Di Fiore
Frédéric
F
Gangloff
Alice Oden
AO
Ciardiello
Fortunato
F
Pfeiffer
Per
P
Qvortrup
Camilla
C
Hansen
Tine Plato
TP
Van Cutsem
Eric
E
Piessevaux
Hubert
H
Lambrechts
Diether
D
Delorenzi
Mauro
M
Tejpar
Sabine
S
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols; D014408:Biomarkers, Tumor / Q000235:genetics*; D000068818:Cetuximab; D058534:Class I Phosphatidylinositol 3-Kinases; D015179:Colorectal Neoplasms / Q000188:drug therapy* / Q000235:genetics*; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics*; D016016:Proportional Hazards Models; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D012372:ROC Curve; D012189:Retrospective Studies; D016019:Survival Analysis
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D014408:Biomarkers, Tumor; D019869:Phosphatidylinositol 3-Kinases; D058534:Class I Phosphatidylinositol 3-Kinases; C484760:PIK3CA protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D000068818:Cetuximab