Mucositis is not only one of the most unpleasant toxicities of cancer treatment, but it reduces quality of life, as well as causing treatment delays, dose reductions and increasing healthcare costs. Its occurrence, anywhere in the oro-digestive tract, is not easy to predict, depending as it does on a combination of patient, tumour and treatment factors. Lung cancer chemotherapy can lead to oral, oesophageal and lower gastrointestinal mucositis, while Radiation therapy causes oesophageal mucositis, and may increase diarrhoea. The introduction of targeted anti-cancer agents has further complicated the field, with EGRF inhibitors increasing diarrhoea and causing rash. mTOR inhibitor-induced stomatitis resembles aphthous ulceration and cannot be treated as “standard” mucositis. The colitis from immune checkpoint inhibitors is different again, and brings greater challenges in management. Evidence-based management strategies are lacking, and much work is needed. 

Mucositis (or indeed any single toxicity) rarely occurs in isolation, being especially commonly linked with nausea, chills, taste alteration and dehydration. A cluster of respiratory toxicities includes pain, cough, palpitation, infection and dyspnoea, all of which are particularly problematic in lung cancer patients, and which significantly reduce quality of life. The ability to target the mechanism of a cluster of toxicities may lead to strategies to reduce the impact of the entire cluster. Toxicity risk prediction in parallel with tumour-response prediction would lead to the best quality outcomes for patients.