Inclusion Criteria:  Written informed consent prior to initiation of any study procedures and willingness and ability to comply with the study schedule Any patient ≥18yrs who has received 6 months of pembrolizumab treatment with or without chemotherapy for advanced Non small cell lung cancer who is planned to continue immunotherapy treatment because of continued benefit.  Exclusion Criteria:  Disease progression or not tolerating treatment at 6 months into therapy Clinician does not intend to continue immunotherapy