Assess Efficacy & Safety of Selumetinib in Combination With Docetaxel in Patients Receiving 2nd Line Treatment for v-Ki-ras2 Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS) Positive NSCLC

Inclusion Criteria: * Provision of signed, written and dated informed consent prior to any study specific procedures * Male or female, aged 18 years or older * Histological or cytological confirmation of locally advanced or metastatic NSCLC (IIIB-IV) * KRAS mutation positive tumour sample as determined by the designated testing laboratory * Failure of 1st line anti-cancer therapy due to radiological documentation of disease progression in advanced disease or subsequent relapse of disease following 1st line therapy Exclusion Criteria: * Mixed small cell and non-small cell lung cancer histology. * Received \>1 prior anti-cancer drug regimen for advanced or metastatic NSCLC. Patients who develop disease progression while on switch maintenance therapy (maintenance using an agent not in the first-line regimen) will not be eligible. * Receiving or have received systemic anti-cancer therapy within 30 days prior to starting study treatment * Other concomitant anti-cancer therapy agents excepts steroids * Prior treatment with a Mitogen-Activated protein Kinase (MEK) inhibitor or any docetaxel-containing regimen (prior treatment with paclitaxel is acceptable). * Last radiation therapy within 4 weeks prior starting study treatment, or limited field of radiation for palliation within 7 days of the first dose of study treatment