What was the initial cancer indication for keytruda's fda clearance?

What cancer did Keytruda (pembrolizumab) get FDA approval for first?

Keytruda’s initial FDA clearance was for unresectable or metastatic melanoma. The FDA approval was specifically for patients with melanoma that had progressed after ipilimumab (Yervoy) and, if they had a BRAF V600 mutation, after a BRAF inhibitor. [1]

Was it first approved for melanoma, or another tumor type?

It was first approved for melanoma rather than a different solid tumor indication. Later approvals expanded Keytruda to additional cancers and combination regimens, but the first FDA indication was melanoma with prior-treatment requirements. [1]

Where can I verify the original indication details?

The original indication wording and approval context are listed in the FDA approval record for Keytruda’s first approval. [1]

Sources:
[1] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=125514