The “ESO-ESMO-RCE Clinical Update on Rare Adult Solid Cancers” is an educational effort held on an annual basis and conceived to strengthen the education of medical professionals willing to devote their career to rare cancers. Despite being rare as single entities, rare adult solid cancers account for as many as 15% of all new cancer cases, thus being the main group within rare cancers in general. The definition of rare cancers by the RARECARE project and the list of the 10 “families” of rare adult solid cancers gave rise to shape the sessions of this course: – Head & neck cancers – Sarcomas – Rare thoracic tumors – Neuroendocrine tumors – Central nervous system neoplasms – Rare female genital cancers – Endocrine gland tumors – Digestive rare cancers – Rare urological and male genital tumors – Rare skin cancers & non-cutaneous melanoma Since ‘networking’ and ‘multidisciplinarity’ are the two main keywords to improve the quality of care of rare cancers, ESO has decided to develop the programme of this course in collaboration with other European initiatives in this field and to give its contribution to tackle the rare cancer issue. The 6th ESO-ESMO-RCE Clinical Update on Rare Adult Solid Cancers was conceived in the context of, and supported by, EURACAN, the European Reference Network on rare adult solid cancers. The Faculty has been largely selected from EURACAN, also with the aim of letting this educational effort closely interact with its networking activities. Optimal management of rare adult solid cancers poses specific diagnostic and therapeutic challenges. The sessions of the course have been designed to address the needs of clinical oncologists wanting an update on recent advancements on these tumours. The course will be held online and we have done our best to design a programme enabling participants to attend according to their own schedule. There has been a mixture of pre-recorded sessions and live sessions for Q&A and clinical case discussions with faculty members and moderators.