Strategies to minimize and mitigate external beam radiation therapy related mucositis and pain during the treatment of head and neck cancer remain limited. The investigators hypothesize that gabapentin could be used to delay or reduce treatment-related pain, reliance on opioid medication, and improve the quality of life for these patients.

The specific aims of this proposed study include the following:

• Evaluate the reduction or delay of mucositis related pain and morbidity with the use of gabapentin in patients with stage III or IV oropharyngeal squamous cell carcinoma undergoing definitive radiation with concurrent chemotherapy as part of their cancer management, compared to standard supportive side effect mitigation - using patient reported quality of life endpoints such as the Patient-Reported Oral Mucositis Symptoms (PROMS) scale.
• Assess morphine-equivalent opioid use in both treatment arms by collecting the patient's narcotic use in the previous 24-hour period at each weekly evaluation during radiation treatment.
• Report on change in Speech and swallow performance, as measured by the Performance Status Scale (PSS) for Head and Neck Cancer Patients
• Evaluate changes in weight from baseline throughout treatment between the two arms.
• Assess feeding tube requirements during treatment.
• Evaluate the adverse events associated with gabapentin.
• Evaluate the severity of radiation mucositis (grade 3-4, CTCAE, v. 4)

Inclusion Criteria:

• Patients being treated with combination chemotherapy and radiation therapy daily for locally advanced (stage III-IV) squamous cell carcinoma of the oropharynx.
• Age ≥ 18.
• ECOG performance status ≤ 1.
• Patients must provide study specific informed consent prior to study entry and be able to fill out toxicity and quality of life related questionnaires.

Exclusion Criteria:

• Patients may not be receiving gabapentin, any other investigational agents, or other anticonvulsants.
• Patients with metastatic disease are excluded from this clinical trial.
• Patient with allergies or hypersensitivity to gabapentin.
• Patients receiving surgery as part of their definitive management.
• Patients who have received prior chemotherapy or radiation therapy.
• Patients unable to complete the required forms; however, verbal completion is adequate if recorded on the form daily.
• Uncontrolled serious illness including, but not limited to, ongoing or serious active infection requiring IV antibiotics for over 30 days, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia other than chronic, stable atrial fibrillation, or psychiatric illness/social situations that would limit compliance with study requirements.

Adverse effects data were collected from baseline, throughout the 7 week treatment course, and at the 6-week post-treatment follow-up timepoint. Thus, this time period was about 14 weeks.