 The clinical benefit of this treatment is limited due to development of drug resistance in 6-8 months for treatment with BRAFi and 9-14 months for treatment with BRAFi in combination with MEKi.This is often associated with secondary mutations in the MAPK pathway leading to re-activation of the pathway.Withholding from treatment with BRAFi andor MEKi leads to a reversible hyperactivation of the MAPK pathway, causing a transient growth arrest. Chronic proliferation and growth arrest occur when there is a persistent hyperactivation of the MAPK pathway. Treatment of BRAFi andor MEKi resistant melanoma with vorinostat, a histone deacetylase inhibitor HDACi, leads to persistent hyperactivation of the pathway and a state of growth arrest with hallmarks of oncogene induced senescence.In these studies in mice with BRAFi resistant BRAF V600 mutated melanoma switch from a BRAFi to the HDACi vorinostat resulted in complete disappearance of the tumor after two months of treatment. 