In fact, the study found that Supportive-Expressive Therapy (SET) was beneficial and had no demonstrable harms.
It is important to note that the study focused on the effectiveness of SET compared to a control group, and the focus was on measuring improvements in mood and quality of life. While the study did not find any harms, it's possible that certain individuals might experience unforeseen or individual reactions to therapy. However, the results of the study were highly positive, and it is considered a cornerstone of psychosocial interventions for cancer patients.
If you have any concerns about potential harms related to therapy, you should always consult with a qualified mental health professional.