An 80-year-old woman developed mucositis during treatment with pembrolizumab for metastatic nodular melanoma. The woman with a history of recurrent right cheek nodular melanoma and lung metastasis, depression, diabetes mellitus type 2 and hypertension presented with worsening dysphagia and odynophagia for one month. She was diagnosed with nodular melanoma in July 2015. In December 2016 she had metastasis of the melanoma. Then she underwent modified radical neck dissection, right superficial parotidectomy and excision of right subcutaneous peri-mandibular facial mass in January 2017. In February, she started adjuvant ipilimumab and local radiation therapy. However, she developed severe diarrhoea and rash following 2 doses of ipilimumab. Thus, the ipilimumab was discontinued. In March 2018, she developed metastatic lesion in right lung. Therefore, pembrolizumab [dosage and route not stated] and radiation therapy were initiated. Following 3 doses she was noted with near resolution of right lung metastatic lesion. In October 2018, PET scan showed metabolic activity in right supraglottic area. She was admitted in a hospital and underwent direct laryngoscopy, which revealed a developed posterior supraglottic mass with inflamed mucosa encroached over posterior supraglottic airway and generalised inflamed mucosa throughout lower pharynx. Biopsy revealed friable purulent debris with focal multinucleated giant cells without any evidence infection or melanoma cells. She was suspected with immunotherapy associated mucositis.The woman's pembrolizumab treatment was discontinued. She started oral prednisone 40 mg/day. Her symptoms were improved. Then she was discharged with prednisone slow taper. However, 2 months later she developed throat swelling with hoarseness and new oxygen requirement. Neck CT revealed near complete occlusion of airway due to tissue thickening of larynx and epiglottis. Direct laryngopharyngoscopy revealed impending airway obstruction with massive swelling of posterior supraglottic larynx and diffuse inflamed granular mucosa involving lower larynx and supraglottic larynx. Histologic examination of tissue biopsies showed fibrinopurulent exudate and granulation tissue with acute and chronic inflammation in left and right arytenoid tissues of the larynx and also epiglottic tissue. She was negative for infectious aetiology and malignancy. Thus, diagnosis of grade 4 pembrolizumab-induced mucositis was confirmed. She developed agitation and impaired fasting glucose due to the prednisone. She also had slow improvement with prednisone. Therefore, she was started on infliximab with concurrent oral prednisone 40 mg/day. Following the first dose of infliximab she had significant improvement. The prednisone dose was tapered 5mg for every 3 weeks. Her supraglottic soft tissue was improved remarkably after 2 doses of infliximab. Follow-up flexible fiberoptic laryngopharyngoscopy revealed clear nasal cavities, clear nasopharynx with some improvement of mucosa of upper larynx and lower pharynx. Posterior supraglottic mas...