Part 3: ORR

Part 3: Gem/Cis/Intermittent Pemigatinib 9 mg

Participants received gemcitabine (Gem) intravenously starting at 1000 mg/meters squared (m\^2) on Days 1 and 8 of each 21-day cycle. Cisplatin (Cis) was administered intravenously starting at 70 mg/m\^2 once every 3 weeks on Day 1 of each 21-day cycle. Both gemcitabine and cisplatin doses could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued chemotherapy with medical monitor approval. Participants self-administered oral pemigatinib 9 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of gemcitabine/cisplatin.

Part 3: Gem/Cis/Intermittent Pemigatinib 13.5 mg

Participants received gemcitabine intravenously starting at 1000 mg/m\^2 on Days 1 and 8 of each 21-day cycle. Cisplatin was administered intravenously starting at 70 mg/m\^2 once every 3 weeks on Day 1 of each 21-day cycle. Both gemcitabine and cisplatin doses could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued chemotherapy with medical monitor approval. Participants self-administered oral pemigatinib 13.5 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of gemcitabine/cisplatin.

Part 3: Tras/Intermittent Pemigatinib 13.5 mg

Trastuzumab (Tras) was administered as an open-label, commercial product at an initial intravenous dose of 8 mg/kilograms (kg), followed by 6 mg/kg intravenously once every 3 weeks. The dose could have been adjusted for toxicity management, per commercial labeling. The investigator could have interrupted, modified, or discontinued trastuzumab with medical monitor approval. Participants self-administered oral pemigatinib 13.5 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of trastuzumab.

Part 3: Doc/Intermittent Pemigatinib 13.5 mg

Participants received docetaxel (Doc) intravenously starting at 75 mg/m\^2 once every 3 weeks on Day 1 of each cycle. The dose could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued chemotherapy with medical monitor approval. Participants self-administered oral pemigatinib 13.5 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of docetaxel.

Part 3: Pem/Intermittent Pemigatinib 9 mg

Participants received pembrolizumab (Pem) intravenously at 200 mg once every 3 weeks on Day 1 of each cycle. The dose could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued pembrolizumab with medical monitor approval. Participants self-administered oral pemigatinib 9 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of pembrolizumab.

Part 3: Pem/Intermittent Pemigatinib 13.5 mg

Participants received pembrolizumab intravenously at 200 mg once every 3 weeks on Day 1 of each cycle. The dose could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued pembrolizumab with medical monitor approval. Participants self-administered oral pemigatinib 13.5 mg QD on a 2-weeks-on therapy and 1-week-off therapy schedule. The treatment cycle consisted of: Days 1 through 14: pemigatinib QD; Days 15 through 21: treatment break. It was permissible to continue pemigatinib administration during the toxicity break of pembrolizumab.

Part 3: Pem/Continuous Pemigatinib 13.5 mg

Participants received pembrolizumab intravenously at 200 mg once every 3 weeks on Day 1 of each cycle. The dose could have been adjusted for toxicity management per commercial labeling. The investigator could have interrupted, modified, or discontinued pembrolizumab with medical monitor approval. Participants self-administered oral pemigatinib 13.5 mg QD on Days 1 through 21 of each 21-day cycle. It was permissible to continue pemigatinib administration during the toxicity break of pembrolizumab.

Part 3: Ref/Continuous Pemigatinib 9 mg

Retifanlimab (Ref) was administered once every 4 weeks on a 28-day cycle as an open-label product, at an initial intravenous dose of 500 mg. Participants self-administered oral pemigatinib 9 mg QD on Days 1 through 21 of each 21-day cycle.

Part 3: Ref/Continuous Pemigatinib 13.5 mg

Retifanlimab was administered once every 4 weeks on a 28-day cycle as an open-label product, at an initial intravenous dose of 500 mg. Participants self-administered oral pemigatinib 13.5 mg QD on Days 1 through 21 of each 21-day cycle

Part 3: Ref/Continuous Pemigatinib 20 mg

Retifanlimab was administered once every 4 weeks on a 28-day cycle as an open-label product, at an initial intravenous dose of 500 mg. Participants self-administered oral pemigatinib 20 mg QD on Days 1 through 21 of each 21-day cycle.

Analysis denominator · Participants