Microsatellite instability, mismatch repair deficiency, and BRAF mutation in treatment-resistant germ cell tumors.
OBJECTIVE
Mismatch repair (MMR) deficiency and microsatellite instability (MSI) are associated with cisplatin resistance in human germ cell tumors (GCTs). BRAF mutation (V600E) is found in MSI colorectal cancers. The role of RAS/RAF pathway mutations in GCT treatment response is unknown.


METHODS
Two patient cohorts were investigated: 100 control GCTs (50 seminomas and 50 nonseminomas) and 35 cisplatin-based chemotherapy-resistant GCTs. MMR proteins were analyzed by immunohistochemistry, and eight microsatellite loci were examined for MSI. Tumors were assessed for specific BRAF and KRAS mutations.


RESULTS
Resistant tumors showed a higher incidence of MSI than controls: 26% versus 0% in two or more loci (P < .0001). All resistant tumors were wild-type KRAS, and two controls (2%) contained a KRAS mutation. There was a significantly higher incidence of BRAF V600E mutation in resistant tumors compared with controls: 26% versus 1% (P < .0001). BRAF mutations were highly correlated with MSI (P = .006), and MSI and mutated BRAF were correlated with weak or absent staining for hMLH1 (P = .017 and P = .008). Low or absent staining of hMLH1 was correlated with promoter hypermethylation (P < .001). Tumors lacking expression of hMLH1 or MSH6 were significantly more frequent in resistant GCTs than in controls (P = .001 and 0.0036, respectively). Within the subgroup of resistant tumors, patients with MSI showed a trend to longer progression-free survival (P = .068).


CONCLUSIONS
We report for the first time a correlation between a gene mutation--BRAF V600E--and cisplatin resistance in nonseminomatous GCTs. Furthermore, a correlation between MMR deficiency, MSI, and treatment failure is confirmed.
Honecker
Friedemann
F
Department of Oncology, University Medical Center Hamburg- Eppendorf, Hamburg, Germany.
Wermann
Hendrik
H
Mayer
Frank
F
Gillis
Ad J M
AJ
Stoop
Hans
H
van Gurp
Ruud J L M
RJ
Oechsle
Karin
K
Steyerberg
Ewout
E
Hartmann
Jörg Th
JT
Dinjens
Winand N M
WN
Oosterhuis
J Wolter
JW
Bokemeyer
Carsten
C
Looijenga
Leendert H J
LH
D048868:Adaptor Proteins, Signal Transducing / Q000032:analysis; D000251:Adenosine Triphosphatases / Q000032:analysis; D000293:Adolescent; D000328:Adult; D000368:Aged; D002945:Cisplatin / Q000627:therapeutic use; D053843:DNA Mismatch Repair; D045643:DNA Repair Enzymes / Q000032:analysis; D004268:DNA-Binding Proteins / Q000032:analysis; D019008:Drug Resistance, Neoplasm; D006801:Humans; D019656:Loss of Heterozygosity; D008297:Male; D053842:Microsatellite Instability; D008875:Middle Aged; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D009154:Mutation; D009373:Neoplasms, Germ Cell and Embryonal / Q000188:drug therapy / Q000235:genetics*; D009687:Nuclear Proteins / Q000032:analysis; D011518:Proto-Oncogene Proteins / Q000235:genetics; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D016283:Proto-Oncogene Proteins p21(ras); D013736:Testicular Neoplasms / Q000188:drug therapy / Q000235:genetics*; D018631:ras Proteins / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D004268:DNA-Binding Proteins; C117307:KRAS protein, human; C501486:MLH1 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D000251:Adenosine Triphosphatases; C094934:PMS2 protein, human; D000070976:Mismatch Repair Endonuclease PMS2; D000070957:MutL Protein Homolog 1; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins; D045643:DNA Repair Enzymes; D002945:Cisplatin