Identification of multiple mechanisms of resistance to vemurafenib in a patient with BRAFV600E-mutated cutaneous melanoma successfully rechallenged after progression.
OBJECTIVE
To investigate the mechanism(s) of resistance to the RAF-inhibitor vemurafenib, we conducted a comprehensive analysis of the genetic alterations occurring in metastatic lesions from a patient with a BRAF(V600E)-mutant cutaneous melanoma who, after a first response, underwent subsequent rechallenge with this drug.


METHODS
We obtained blood and tissue samples from a patient diagnosed with a BRAF(V600E)-mutant cutaneous melanoma that was treated with vemurafenib and achieved a near-complete response. At progression, he received additional lines of chemo/immunotherapy and was successfully rechallenged with vemurafenib. Exome and RNA sequencing were conducted on a pretreatment tumor and two subcutaneous resistant metastases, one that was present at baseline and previously responded to vemurafenib (PV1) and one that occurred de novo after reintroduction of the drug (PV2). A culture established from PV1 was also analyzed.


RESULTS
We identified two NRAS-activating somatic mutations, Q61R and Q61K, affecting two main subpopulations in the metastasis PV1 and a BRAF alternative splicing, involving exons 4-10, in the metastasis PV2. These alterations, known to confer resistance to RAF inhibitors, were tumor-specific, mutually exclusive, and were not detected in pretreatment tumor samples. In addition, the oncogenic PIK3CA(H1047R) mutation was detected in a subpopulation of PV1, but this mutation did not seem to play a major role in vemurafenib resistance in this metastasis.


CONCLUSIONS
This work describes the coexistence within the same patient of different molecular mechanisms of resistance to vemurafenib affecting different metastatic sites. These findings have direct implications for the clinical management of BRAF-mutant melanoma.
Authors' Affiliations: Department of Oncology, University Hospital of Lausanne; Genomic Technologies Facility (GTF), Center for Integrative Genomics, University of Lausanne; Vital-IT, Swiss Institute of Bioinformatics, and the Ludwig Center for Cancer Research of the University of Lausanne, Lausanne, Switzerland.
Emanuela
E
Romano
Sylvain
S
Pradervand
Alexandra
A
Paillusson
Johann
J
Weber
Keith
K
Harshman
Katja
K
Muehlethaler
Daniel
D
Speiser
Solange
S
Peters
Donata
D
Rimoldi
Olivier
O
Michielin
D000328:Adult; D017398:Alternative Splicing; D019943:Amino Acid Substitution; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D003062:Codon; D018450:Disease Progression; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D059472:Exome; D020869:Gene Expression Profiling; D023061:Gene Order; D059014:High-Throughput Nucleotide Sequencing; D006801:Humans; D007211:Indoles / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D008545:Melanoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D009154:Mutation; D009362:Neoplasm Metastasis; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D012878:Skin Neoplasms; D013449:Sulfonamides / Q000494:pharmacology* / Q000627:therapeutic use; D000077484:Vemurafenib; D000096142:Cutaneous Malignant Melanoma
D000970:Antineoplastic Agents; D003062:Codon; D007211:Indoles; D013449:Sulfonamides; D000077484:Vemurafenib; D048493:Proto-Oncogene Proteins B-raf