Background <p>The modified German guardianship law (<i>Betreuungsrecht</i>) from 2023 stipulates that a&#xa0;person’s wishes regarding medical, nursing or psychosocial treatment, in combination with the medical indication, legitimise the implementation of the measures. In the field of oncology, this issue is particularly relevant in order to treat people according to their wishes while at the same time focusing on the medical indication.</p> Methods <p>A&#xa0;pragmatic search using the keywords “advance care planning”, “oncology” and “shared decision making” was conducted in medical databases.</p> Results <p>Advance care planning (ACP) describes a&#xa0;structured, systematic discussion process. The aim of the ACP discussion process is to ensure that patients are treated reliably and in accordance with their individual values, preferences and treatment preferences in the event of incapacity to give consent, for example as a&#xa0;result of acute health crises or as a&#xa0;consequence of oncological diseases.</p> Conclusion <p>Particularly in cancer treatment, shared decision-making should take place within an interprofessional team, as treatment preferences can be better determined with cancer patients in view of their individual assessment of quality of life.</p>