Malignant melanoma (MM) patients are being treated with an increasing number of personalized medicine (PM) drugs, several of which are small molecule drugs developed to treat patients with specific disease genotypes and phenotypes. In particular, the clinical application of protein kinase inhibitors (PKI) has been highly effective for certain subsets of MM patients. Vemurafenib, a PKI targeting BRAF mutated protein, has shown significant efficacy in slowing disease progression. In this paper we provide an overview of this new generation of targeted drugs, and demonstrate the first data on localization of personalized medicine drugs within tumor compartments. In this study, we have introduced matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to provide new information on one of the drugs currently used in the PM treatment of MM, vemurafenib. In a proof-of-concept in vitro study, MALDI-MSI was used to identify vemurafenib applied to metastatic lymph nodes tumors of subjects attending the regional hospital network of Southern Sweden. The paper provides evidence of BRAF overexpression in tumors isolated from MM patients and localization of the specific drug targeting BRAF, vemurafenib, using mass spectrometry fragment ion signatures. Our ability to determine drug uptake at the target sites of directed therapy provides important opportunity for increasing our understanding about the mode of action of drug activity within the disease environment.