Any prior systemic anti-cancer therapy for the treatment of this current diagnosis, An investigational drug within 30 days of starting treatment or within five half-lives of the compound (whichever is the most appropriate is at the discretion of the Investigator), or have not recovered from side effects of an investigational drug Any non-systemic anti-cancer therapy which has not been cleared from the body by the time of starting study treatment Radiation therapy within 4 weeks prior to starting study treatment, or limited field of radiation for palliation within 7 days of the first dose of study treatment Major surgery within 4 weeks prior to entry into the study (excluding the placement of vascular access) which would prevent administration of study treatment, Any prior investigational therapy comprising inhibitors of RAS, RAF or MEK at any time, Previous treatment with dacarbazine. Any unresolved toxicity >CTCAE grade 2 from previous anti-cancer therapy, excluding alopecia -History of allergic reactions attributed to compounds of similar chemical or biologic composition to selumetinib or dacarbazine