The MEK1P124L allele was identified in a 55-year-old male with metastatic melanoma, including pulmonary and skeletal involvement at the time of clinical trial enrollment...In accordance with protocol specifications, the patient was switched to the AZD6244 treatment arm. This resulted in regression or stabilization of all disease sites except for a left axillary lymph node metastasis...MEK1P124L was detected in this specimen. Following resection, the patient continued on AZD6244 and showed prolonged disease stabilization (>44 weeks), including a steadily declining RECIST score and a 28% overall reduction in tumor burden (Fig. 3D).