Intratumoral Molecular Heterogeneity in a <i>BRAF</i>-Mutant, BRAF Inhibitor-Resistant Melanoma: A Case Illustrating the Challenges for Personalized Medicine

Targeted therapies are increasingly being used to treat a variety of cancers. Their efficacy depends upon the accurate detection and targeting of a specific mutation or aberration in the tumor. All cancers, such as melanoma, are molecularly heterogeneous, with drug-resistant subclones present before the treatment or emerging as a result of targeted therapies. Here, we show intralesional molecular heterogeneity in a progressing V600E BRAF-mutant melanoma metastasis from a patient treated for 7 months with the BRAF inhibitor vemurafenib. In the single metastasis, two distinct subclones were observed, both V600E BRAF-mutant and only one with an additional G13R NRAS mutation. Molecular heterogeneity even at the intralesional level shows that personalizing or adjusting therapies based on genotyping of a portion of a single lesion may not accurately depict the molecular profile or drivers of oncogenesis across the entire patient's melanoma.