The purpose of the phase 3, clinical study is to determine if GC4419 (avasopasem manganese) administered prior to intensity-modulated radiation therapy (IMRT) reduces the severity of radiation induced oral mucositis in patients who have been diagnosed with locally advanced, non-metastatic squamous cell carcinoma of the head and neck.

Inclusion Criteria:

• squamous cell carcinoma of the head and neck
• treatment plan to receive IMRT delivered as single daily fractions of 2.0 to 2.2 Gy with a cumulative radiation dose of 60-72 Gy
• Treatment plan to receive standard cisplatin monotherapy
• Age 18 years or older
• Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2
• Adequate hematologic, renal and liver function
• Negative serum pregnancy test
• Use of effective contraception

Exclusion Criteria:

• Tumor of the lips, larynx, hypopharynx, nasopharynx, sinuses, or salivary glands
• Metastatic disease
• Prior radiotherapy to the region of the study cancer or adjacent anatomical
• Prior induction chemotherapy
• Receiving any approved or investigational anti-cancer agent other than those provided for in this study
• Concurrent participation in another interventional clinical study
• Inability to eat soft solid food at baseline
• Malignant tumors other than HNC within the last 5 years
• Active infectious disease excluding oral candidiasis
• Presence of oral mucositis at baseline
• Known history of HIV or active hepatitis B/C
• Female patients who are pregnant or breastfeeding
• Known allergies or intolerance to cisplatin and similar platinum-containing compounds
• Requirement for concurrent treatment with nitrates or other drugs that may create a risk for a precipitous decrease in blood pressure