Feasibility Study of MET-4: Evaluating Fecal Microbiome Effects in Immunotherapy Patients

Inclusion Criteria: * Signed written and voluntary informed consent * Age \>=18 years, male or female * Histologically or cytological documented locally-advanced or metastatic solid malignancy which is incurable. * Group A: Is already on treatment with monotherapy anti-PD-1 or PD-L1 immune checkpoint inhibitor, not in the context of a therapeutic clinical trial. Group B: Is intended to start on treatment with monotherapy anti-PD-1 or PD-L1 immune checkpoint inhibitors as considered appropriate by treatment physician, and not in the context of a therapeutic clinical trial. Group C: Is already on treatment with monotherapy anti-PD-1 or PD-L1 immune checkpoint inhibitor, not in the context of a therapeutic clinical trial with first unconfirmed PD on evaluation scan per investigator's assessment. * Be willing to provide 10-15 unstained slides of archival tissue sample. Subjects who decline or have not sufficient archived tissue samples may still enroll if all other criteria are eligible. * Be willing and able to provide stool and blood specimen for analyses at protocol specified time points. * Have measurable disease based on RECIST 1.1 * Performance status of 0-2 on the Eastern Cooperative Oncology Group (ECOG) performance scale. * Prior therapy with any immunotherapy allowed. * Not pregnant for females of child bearing potential as indicated by negative serum or urine pregnancy test within 72 hours of study start. Exclusion Criteria: * Subjects unable to swallow orally administered medications or any subjects with gastrointestinal disorders likely to interfere with absorption (e.g. bowel obstruction, short gut syndrome, blind loop syndrome, ileostomy etc). Subjects with colostomies may be enrolled. * Any condition that, in the opinion of the Investigator, would interfere with subject safety, or evaluation of the collected specimen and interpretation of study result. * Pregnant or planning to get pregnant in the next 6 months.