This trial studies the side effects of pembrolizumab with or without chemotherapy in treating patients with stage IV non-small cell lung cancer that has come back (recurrent) and has spread to other places in the body (advanced). Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Drugs used in chemotherapy, such as pemetrexed and carboplatin, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving pembrolizumab with or without chemotherapy may shrink the tumor in older patients with non-small cell lung cancer.

The primary and secondary objectives of the study:

PRIMARY OBJECTIVE:

I. To estimate the adverse event profile of MK-3475 (pembrolizumab) in non-small cell lung cancer patients who are age 70 years of age or older and who are treated with MK-3475 (pembrolizumab) +/- chemotherapy in a first-line setting.

SECONDARY OBJECTIVES:

I. To estimate overall survival. II. To describe patient quality of life during the treatment using the Linear Analogue Self-Assessment (LASA) questionnaire.

III. To explore whether Comprehensive Geriatric Assessment (CGA) -derived risk score is able to predict rates of severe adverse events in older cancer patients who receive MK-3475 (pembrolizumab) or MK-3475 (pembrolizumab) + chemotherapy.

OUTLINE: Patients are assigned to 1 of 2 groups.

GROUP A: Patients receive pembrolizumab intravenously (IV) over 30 minutes on day 1. Cycles repeat every 21 days in the absence of disease progression or unacceptable toxicity.

GROUP B: Patients receive pembrolizumab IV over 30 minutes, pemetrexed IV over 10 minutes, and carboplatin IV per institutional guidelines on day 1. Cycles repeat every 21 days in the absence of disease progression or unacceptable toxicity.

After completion of study treatment, patients are followed up annually for up to 5 years after registration.

Inclusion Criteria:

• Documentation of Disease: Histologic or cytologic diagnosis of non-small cell lung cancer (adenocarcinoma). Stage IV or recurrent metastatic non-small cell lung cancer. No planned initiation of definitive (potentially curative) concurrent chemo-radiation

• Planning to begin MK-3475 (pembrolizumab) treatment within 14 days of registration, with or without combination chemotherapy. Treating physician considers pembrolizumab as appropriate and plans to proceed with one of the following treatment schedules:

  • MK-3475 (pembrolizumab) 200 mg IV flat dose every 21 days or 400 mg IV every 42 days.
  • MK-3475 (pembrolizumab) 200 mg IV or 400 mg IV + carboplatin area under the curve (AUC) = 5 + pemetrexed 500 mg/m^2 (20% chemotherapy dose reduction is permitted per the discretion of the treating physician)

• Patients will be ineligible if they have an autoimmune disorder, are post-organ transplantation, or are receiving ongoing immunosuppression treatment

• Prior adjuvant therapy is allowed and must have been completed at least 6 months prior to registration

• No planned radiation or other cancer treatment in the 3 months following registration

• No untreated brain metastases. Patients must be off corticosteroids and asymptomatic at registration

• Absolute neutrophil count (ANC) >= 1500/mm^3 (1.5 x 10^9/L)

• Platelet count: >= 100,000/mm^3 (100 x 10^9/L)

• Creatinine >= 30 mL/min* for patients enrolled to pembrolizumab alone and > 45 mL/min for patients enrolled to chemotherapy + pembrolizumab

  * Calculated using the Cockcroft-Gault formula

• Total serum bilirubin =< 1.5 upper limit of normal (ULN) (< 3 ULN if Gilbert's disease)

• Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) =< 3 x ULN (=< 5.0 x ULN if liver metastases present)

• Alkaline phosphatase =< 2.5 x ULN (=< 5 x ULN if bone or liver metastases present) Language: Patients must be able to speak and comprehend English in order to complete the mandatory patient-completed measures