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