A Phase 1a/1b Multicenter, Open-label Dose Escalation/Expansion Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Preliminary Evidence of Antitumor Activity of PLN-101095 as Monotherapy and in Combination With Pembrolizumab in Adult Participants With Advanced or Metastatic Solid Tumors Who Have Disease Progression While on Pembrolizumab

Inclusion Criteria:

1. Has histologically or cytologically confirmed advanced solid tumor
2. Has an advanced or metastatic solid tumor (for which pembrolizumab is indicated) and have evidence of disease progression after treatment with pembrolizumab.
3. At least 1 measurable lesion, as defined by RECIST v1.1
4. Estimated survival of ≥3 months
5. No effective therapeutic options available (eg, has received standard of care or is intolerant of, refuses, or is not eligible for standard of care antineoplastic therapy)

Exclusion Criteria:

1. Any immune-related medical conditions that would put participants at greater risk when receiving pembrolizumab
2. Previous treatment with pembrolizumab <21 days prior to the first dose of combination therapy of pembrolizumab and PLN-101095
3. Received an immunotherapy other than pembrolizumab in the last 4 weeks prior to the first dose of PLN-101095
4. Received radiotherapy (RT) within 1 week for palliative bone-directed therapy and 4 weeks for all other types, prior to the first dose of PLN-101095
5. Received chemotherapy or other targeted therapies within 2 weeks prior to the first dose of PLN-101095
6. Received a cell therapy within the last 12 months prior to the first dose of PLN-101095
7. Known active central nervous system (CNS) metastases (brain and/or leptomeningeal metastases)
8. Pregnant or lactating female participant