Inclusion Criteria:

          -  The participant (or legally acceptable representative if applicable) must provide
             written informed consent for the study. The participant may also provide consent for
             future unspecified research samples. However, the participant may participate in the
             study without participating in the future unspecified research sample collection.

          -  Males and females age ≥ 18 years at the time of consent.

          -  ECOG Performance Status of 0-1 within 28 days prior to registration.

          -  Patients must have undergone complete surgical resection of their stage I NSCLC
             between 4-12 weeks prior to registration and have negative surgical margins (R0).

               -  NOTE: Both squamous and non-squamous histologies are allowed into the study.
                  Cancers with a histology of "adenosquamous" are considered a type of
                  adenocarcinoma and thus "non-squamous histology".

               -  NOTE: Staging will be according to the AJCC 8th edition.

          -  Pathological tumor size must be 1.0 - 4.0 cm in greatest dimension.

          -  Surgery for this lung cancer must be completed at least 28 days prior to registration.

          -  Must have either previous NGS and PD-L1 results available using the Dako 22C3 antibody
             or have archival tissue of surgical specimen from current diagnosis available to
             perform analyses. If prior PD-L1 results with Dako 22C3 antibody are not available
             from a CLIA-accredited laboratory, subjects must be able to provide 5µm x 4unstained
             slides for prospective analysis to be used for stratification. If NGS results are not
             available, subjects must be able to provide at least 10 x 10µm unstained and 1 x 4µm
             H&E slides from current diagnosis for future NGS and/or other genetic analyses.

          -  Demonstrate adequate organ function as defined in the protocol; all screening labs to
             be obtained within 28 days prior to registration.

          -  Females of childbearing potential must have a negative urine or serum pregnancy test
             within 72 hours prior to registration. If the urine test is positive or cannot be
             confirmed as negative, a serum pregnancy test will be required. For subjects
             randomized to the pembrolizumab arm: If there is > 72 hours between the screening test
             and C1D1, another pregnancy test (urine or serum) must be performed and must be
             negative before the subject may start C1D1.

               -  NOTE: Females are considered of childbearing potential unless: they are
                  postmenopausal; are surgically sterile; or they have a congenital or acquired
                  condition that prevents childbearing. See Section 5.1.4 for definitions.

               -  NOTE: Abstinence is acceptable if this is the usual lifestyle and preferred
                  contraception for the subject.

          -  A female participant is eligible to participate if she is not pregnant, not
             breastfeeding, and at least one of the following conditions applies:

               -  Not a woman of childbearing potential (WOCBP) OR

               -  A WOCBP who is using a highly effective contraceptive method (failure rate of <1%
                  per year), or is abstinent from heterosexual intercourse as their preferred and
                  usual lifestyle (abstinent on a long term and persistent basis) during the
                  intervention period and for at least 120 days after the last dose of study drug.
                  The investigator should evaluate the potential for contraceptive method failure
                  (i.e., noncompliance, recently initiated) in relationship to the first dose of
                  study drug. See contraceptive guidance in Section 5.1.4 of the protocol.

          -  As determined by the enrolling physician or protocol designee, ability of the subject
             to understand and comply with study procedures for the entire length of the study

        Exclusion Criteria:

          -  Current lung cancer is <1 cm or > 4 cm in size or is stage II, III, or IV.

          -  Patients with tumors that are known to harbor actionable EGFR mutations.

          -  Prior chemotherapy, radiation therapy, or immunotherapy for the treatment of this lung
             cancer.

          -  Has a known additional malignancy that is progressing or has required active treatment
             within the past 3 years. NOTE: Participants with basal cell carcinoma of the skin,
             squamous cell carcinoma of the skin, or carcinoma in situ (e.g., breast carcinoma in
             situ, cervical cancer in situ) that have undergone potentially curative therapy are
             not excluded.

          -  Prior therapy with an anti-PD-1, anti-PD-L1, or anti-PD-L2 agent or with an agent
             directed to another stimulatory or co-inhibitory T-cell receptor (eg, CTLA-4, OX-40,
             CD137).

          -  Has received a live vaccine within 30 days prior to the first dose of study drug.
             Examples of live vaccines include, but are not limited to, the following: measles,
             mumps, rubella, varicella/zoster (chicken pox), yellow fever, rabies, Bacillus
             Calmette-Guérin (BCG), and typhoid vaccine. Seasonal influenza vaccines for injection
             are generally killed virus vaccines and are allowed; however, intranasal influenza
             vaccines (eg, FluMist®) are live attenuated vaccines and are not allowed.

          -  Is currently participating in or has participated in a study of an investigational
             agent or has used an investigational device within 4 weeks prior to the first dose of
             study treatment.

               -  Note: Participants who have entered the follow-up phase of an investigational
                  study may participate as long as it has been 4 weeks after the last dose of the
                  previous investigational agent.

          -  Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy
             (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of
             immunosuppressive therapy within 7 days prior to randomization.

          -  Has had an allogenic tissue/solid organ transplant.

          -  Has severe hypersensitivity (≥Grade 3) to pembrolizumab and/or any of its excipients.

          -  Has active autoimmune disease that has required systemic treatment in the past 2 years
             (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive
             drugs). Replacement therapy (eg., thyroxine, insulin, or physiologic corticosteroid
             replacement therapy for adrenal or pituitary insufficiency, etc.) is not considered a
             form of systemic treatment.

          -  Has a history of (non-infectious) pneumonitis that required steroids or has current
             pneumonitis.

          -  Has an active infection requiring systemic therapy.

          -  Has a known history of Human Immunodeficiency Virus (HIV). Note: HIV testing is not
             required unless mandated by local health authority.

          -  Has a known history of Hepatitis B (defined as Hepatitis B surface antigen [HBsAg]
             reactive) or known active Hepatitis C virus (defined as HCV RNA [qualitative] is
             detected) infection. Note: Hepatitis B and Hepatitis C testing is not required unless
             mandated by local health authority.

          -  Has active TB (Bacillus Tuberculosis) infection.

          -  Has a history or current evidence of any condition, therapy, or laboratory abnormality
             that might confound the results of the study, interfere with the subject's
             participation for the full duration of the study, or is not in the best interest of
             the subject to participate, in the opinion of the treating investigator.

          -  Has known psychiatric or substance abuse disorders that would interfere with
             cooperation with the requirements of the trial.

          -  Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the study, starting with the screening visit through 120 days
             after the last dose of trial treatment.