Background: Up to 25% of people living with cancer have depression. Existing psychological interventions have limited efficacy in treating depression. Psilocybin, a 5-hydroytrptamintergic psychedelic, coupled with group therapy is safe and effective in ameliorating symptoms of depression (Agrawal et al, ASCO 2022). Response to psilocybin treatment was observed in 83.3% of patients at 8 weeks, and 50% of patients showed full remission of depressive symptoms. This study evaluates the efficacy of psilocybin-assisted group therapy in relieving depression in cancer patients over 18 months. Methods: Adults with curable or metastatic cancer and MDD (according to DSM-5) underwent psychological assessments at baseline. They were treated with single-dose psilocybin 25 mg administered simultaneously in group cohorts of 3-4, supported with group and individual psychological therapy, and evaluated at 8 weeks and 18 months. Primary objectives were long-term effectiveness on depression and anxiety severity (as measured by change in Montgomery Asberg Depression Rating Scale [MADRS] and Hamilton Depression Rating Scale [HAM-A] scores by independent rater assessments) as well as clinical response (≥50% decrease in MADRS total score from baseline to 18 months) and remission (defined as patients with a MADRS total score ≤10 at 18 months). Results: Of 30 patients enrolled in the parent study, 2 died and 4 were lost to follow-up. Clinical response was demonstrated in 18/28 patients (64.2%) from baseline to 18 months follow-up (see table); 16/28 patients (57.1%) demonstrated remission of depression at 18 months. In 24 evaluable patients, continued reduction in mean depression severity scores was also demonstrated from baseline to week 8 (MADRS by 20.6 points [95% CI 23.2, 18.0, p < 0.001] and HAMA-A by 16.7 points [95% CI 19.7, 13.7, p < 0.001]) and from baseline to 18 months (MADRS by 16.7 points [95% CI 20.4, 12.9, p < 0.001] and HAMA-A by 14.4 points [95% CI 17.3, 11.4, p < 0.001]). Conclusions: Long-term follow-up suggests continued robust clinical response and remission from depression with a single dose of psilocybin and simultaneous psychological support in patients with cancer and MDD. These findings indicate psilocybin may play a role in treatment of depression in cancer patients, and further investigations are ongoing.