This study aims to learn more about whether the experimental medication osimertinib (TAGRISSO) is more effective than placebo in participants with Epidermal Growth Factor Receptor (EGFR) mutated stage IA2 or IA3 non small cell lung cancer (NSCLC) after complete surgical removal of the tumor. 

Some lung cancers are due to particular mutations (changes) in the DNA (genetic material), so knowing about the mutations can help doctors decide the best treatment for their patients. One type of mutation that can occur is called the Epidermal Growth Factor Receptor (EGFR) mutation. When a tumor is found to have this type of mutation, there is a class of drugs known as EGFR tyrosine kinase inhibitors (TKIs) which target the mutation to treat the patient.

Osimertinib is an EGFR TKI that targets EGFR mutations. The drug is approved by the U.S. Food and Drug Administration (FDA), although some parts of this study are considered experimental because osimertinib has not yet been approved for use when given as a treatment to prevent recurrence after surgery. 

Participants will be randomized into one of two treatment groups. Randomization is like flipping a coin and there is a 50/50 chance of being assigned to either group. One group will receive 80 mg of osimertinib once a day and the other will receive 80 mg of placebo once a day. The placebo looks just like the study drug, but contains no active ingredients.

Total study participation may last for up to 3 years.