BackgroundSince 2016, France is the only country in the World where continuous deep sedation until death (CDSUD) is regulated by law. CDSUD serves as a response to refractory suffering in palliative situations where the patients’ death is expected to occur in the following hours or days. Little is known on the psychological adjustment surrounding a CDSUD procedure for healthcare providers (HCPs) and relatives. Our study aims to gather qualitative and quantitative data on the specific processes behind the psychological adjustment of both relatives and HCPs, after the administration of CDSUD for patients with cancer.MethodsThe APSY-SED study is a prospective, longitudinal, mixed-methods and multicenter study. Recruitment will involve any French-speaking adult cancer patient for who a CDSUD is discussed, their relatives and HCPs. We plan to include 150 patients, 150 relatives, and 50 HCPs. The evaluation criteria of this research are: 1/ Primary criterion: Psychological adjustment of relatives and HCPs 6 and 13 months after the death of the patient with cancer (psychological adjustment = intensity of anxiety, depression and grief reactions, CDSUD-related distress, job satisfaction, Professional Stress and Professional experience). Secondary criteria: a)occurrence of wish for a CDSUD in patients in palliative phase; b)occurrence of wish for hastened death in patients in palliative phase; c)potential predictors of adjustment assessed after the discussion concerning CDSUD as an option and before the setting of the CDSUD; d) Thematic analysis and narrative account of meaning-making process concerning the grief experience.DiscussionThe APSY-SED study will be the first to investigate the psychological adjustment of HCPs and relatives in the context of a CDSUD procedure implemented according to French law. Gathering data on the grief process for relatives can help understand bereavement after CDSUD, and participate in the elaboration of specific tailored interventions to support HCPs and relatives. Empirical findings on CDSUD among patients with cancer in France could be compared with existing data in other countries and with results related to other medical fields where CDSUD is also conducted.Trial registrationThis protocol received the National Registration Number: ID-RCB2021-A03042-39 on 14/12/2021.