In this research study erlotinib will be given to eligible participants whose lung cancer has been removed by surgery. Eligible patients have adenocarcinoma, a type of non-small lung cancer, and must have 1 or more of the following characteristics: be female, be of Asian or Pacific Rim descent and/or be a never smoker. The potential participant's tumor will be examined for Epidermal growth factor (EGFR) mutations. EGFR is a protein that is overexpressed in most non-small cell lung cancers. Some EGFR has been found to have specific mutations and the participant must have one of these mutations in his tumor.

Erlotinib blocks this protein and may control tumor growth and increase survival. Previous research has shown that erlotinib is most effective for people who have these specific mutations in the EGFR.

• Erlotinib is a pill taken daily and participants may continue to receive erlotinib for up to two years, as long as the cancer does not return and they do not experience any unacceptable side effects.
• While participants are receiving erlotinib, they will be asked to return to the clinic for study visits to monitor the status of their disease and their general health. For the first 5 months of erlotinib, they will return to the clinic monthly. After that they will return to the clinic every three months.

Inclusion Criteria:

• Pathologically confirmed diagnosis of NSCLC of adenocarcinoma histology
• Stage IA-B, IIA-B, or IIIA by the American Joint Committee on Cancer 7th edition staging criteria
• Patients must have undergone surgical resection with curative intent within 6 months of enrollment
• Sufficient tumor tissue available for EGFR mutation analysis
• At least ONE of the following patient characteristics: previously detected deletion 19 or L858R EGFR mutation, female sex, history of never smoking, or Asian/Pacific Rim ethnicity (to be enrolled in the screening portion of trial).
• 18 years of age or older
• Tumor samples must have either exon 19 deletion mutations or the exon 21 L858R point mutation
• ECOG Performance status of 0,1, or 2
• Adequate organ function as outlined in protocol

Exclusion Criteria:

• Radiographic evidence of recurrent NSCLC prior to erlotinib treatment
• Confirmed T790M resistance mutation in the primary tumor sample
• Prior exposure to EGFR tyrosine kinase inhibitors
• Known hypersensitivity to erlotinib, gefitinib, or any closely related drug
• Pregnant or breastfeeding women
• Any evidence of clinically active interstitial lung disease
• Current use of enzyme-inducing anti-epileptic drugs, including carbamazepine, oxcarbazepine, phenytoin, fosphenytoin, phenobarbital, and primidone
• Evidence of any other significant clinical disorder or laboratory finding that makes it undesirable for the patient to participate in the study
• Use of any non-FDA approved or investigational agent within 2 weeks of enrolling onto the trial, or failure to recover from the side effects of any of these agents