Pembrolizumab will be administered.

Carboplatin will be administered.

5-Flurouracil will be administered for over 4-day infusion period.

Cisplatin will be administered.

DOR as assessed by BICR is defined as the time from the date of first documented response (CR or PR) until the date of documented progression or death, whichever comes first, for participants who have PR or CR as best response.

ORR as assessed by the investigator is defined as the percentage of randomized participants achieving CR or PR, as defined by investigator assessment using RECIST v1.1 criteria.

TEAE is defined as any new or worsening adverse event (AE) occurring at or after the initial administration of study treatment through the day of last dose plus 30 days or prior to the start of subsequent anticancer therapy, whichever is earlier, or any follow-up AE with onset date and time beyond 30 days after the last dose of study treatment but prior to the start of subsequent therapy or any AE that is considered treatment-related regardless of the start date of the event.

Blood samples will be collected to determine the laboratory (serum chemistry and hematology) abnormalities.

EORTC QLQ-HN43, is a self-administered, 43-item questionnaire measuring the health-related quality of life (HRQoL) of participants with head and neck cancer. EORTC QLQ-HN43 includes 19 scales (anxiety, body image, coughing, dry mouth and sticky saliva, neurological problems, opening mouth, pain in the mouth, social contact, problems with senses, shoulder problems, skin problems, swelling in the neck, social eating, speech, swallowing, sexuality, problems with teeth, weight loss, and problems with wound healing). Responses to items are rated on a 4-point Likert response scale ranging from 1 "Not at all" to 4 "Very much". Higher scores indicate worse health outcomes.

EORTC QLQ-C30, is a self-administered, 30-item questionnaire measuring the HRQoL of participants with cancer. EORTC QLQ-C30 includes 3 symptom scales (fatigue, pain, and nausea and vomiting), and 6 single items (dyspnea, insomnia, appetite loss, constipation, diarrhea, and financial difficulties). Responses to items 1-28 are rated on a 4-point Likert response scale ranging from 1 "Not at all" to 4 "Very much". Two global health status items are rated on a 7-point numeric rating scale from 1 "Very Poor" to 7 "Excellent." Higher scores indicate greater functioning, better global health status, or more severe symptoms.

EORTC QLQ-C30, is a self-administered, 30-item questionnaire measuring the HRQoL of participants with cancer. EORTC QLQ-C30 includes 5 functional scales (physical, role, cognitive, emotional, and social), 3 symptom scales (fatigue, pain, and nausea and vomiting), a global health status / quality of life scale, and 6 single items (dyspnea, insomnia, appetite loss, constipation, diarrhea, and financial difficulties). Responses to items 1-28 are rated on a 4-point Likert response scale ranging from 1 "Not at all" to 4 "Very much". Two global health status items are rated on a 7-point numeric rating scale from 1 "Very Poor" to 7 "Excellent." Higher scores indicate greater functioning, better global health status, or more severe symptoms.

EORTC QLQ-C30, is a self-administered, 30-item questionnaire measuring the HRQoL of participants with cancer. EORTC QLQ-C30 includes 5 functional scales (physical, role, cognitive, emotional, and social), 3 symptom scales (fatigue, pain, and nausea and vomiting), a global health status / quality of life scale, and 6 single items (dyspnea, insomnia, appetite loss, constipation, diarrhea, and financial difficulties). Responses to items 1-28 are rated on a 4-point Likert response scale ranging from 1 "Not at all" to 4 "Very much". Two global health status items are rated on a 7-point numeric rating scale from 1 "Very Poor" to 7 "Excellent." Higher scores indicate greater functioning, better global health status, or more severe symptoms.

EORTC IL46 is a single item used to measure the overall impact of treatment side effects. Responses are rated on a 4-point Likert response scale ranging from 1 "Not at all" to 4 "Very much." Higher score indicates more impact of treatment side-effects.

Serum concentrations of amivantamab will be analyzed.

Participants who are positive to serum anti-amivantamab antibodies will be reported.