How do you address non-adherence to medical treatment in adolescent and young adult oncology patients due to mental illness such as depression?  

The best answer, I think, is to obtain a thorough child psychiatric evaluation. Noncompliance may arise from a number of different issues, some of which may relate to major mental illnesses such as major depression or anxiety disorders, or more cognitively based concerns such as ADHD or executive fu...

After a good evaluation to ensure that the diagnosis is correct (e.g., unipolar versus bipolar depression, possible role of substance use disorder), treat the mood disorder accordingly. A good, trusting relationship with the provider and other members of the treatment team is also essential. In ad...

Certainly, starting with a thorough evaluation is a given. I would suggest that treatment by a psychiatrist who is also an experienced psychotherapist would be important to maintain continuity of care for this individual, who is likely to be quite fragile.