Effect of Adjuvant Chemotherapy in Highly Malignant Non-Metastatic Prostate Cancer: An Interim Analysis of Non-Randomized Comparative Trials.

PURPOSE/OBJECTIVE(S): Gleason grade group 5 (GG5) prostate cancers is aggressive with high metastatic rates and is not sensitive to androgen deprivation therapy (ADT). Even the presence of a limited (tertiary) Gleason pattern 5 component may have high aggressive biological behavior. This study aims to prospectively evaluate whether a non-androgen receptor pathway therapy - adjuvant chemotherapy could improve clinical outcomes among non-metastatic prostate cancer with the above highly malignant characters.

MATERIALS/METHODS: This prospective non-randomized clinical trial included non-metastatic prostate cancer patients with pathologically proven Gleason score of 9-10 or tertiary Gleason pattern 5. Each subject was allowed to decide whether to receive four to six cycles chemotherapy of docetaxel after receiving a standard treatment (i.e., radical surgery ± radiotherapy or radical radiotherapy combined with long-term ADT). The primary endpoint was event-free survival (EFS). Event was defined as any of biochemical failure or imaging failure, or change of systemic therapy due to PSA arises, or death. The secondary end points were distant metastasis-free survival (MFS), overall survival (OS), and treatment-related adverse events.

RESULTS: A total of 188 consecutive patients were enrolled from November 2019 to November 2022. Median prostate-specific antigen was 26.6 ng/ml. 52% had T3b to T4 disease, 27% had N1 disease. 140 patients received standard therapy only, and 48 patients received adjuvant chemotherapy after radical therapy. The median follow-up time was 18.4 (3.0-36.7) months. The estimated 36-month EFS of the chemotherapy group and the control group were 94.7% vs. 72.8% (p = 0.044). There were 1 event who added novel endocrine therapy in the chemotherapy group, and 21 events in the control group, including 6 cases of biochemical recurrence and 9 cases of lymph node and distant metastasis, 4 cases that changed systemic therapy and 2 cases died. The MFS of the two groups at 36 months were 100% and 90.7%, respectively (P = 0.143). After the 1:1 propensity score match, the EFS and MFS of the two groups were 94.7% and 80.8% (P = 0.069), and 100% and 93.1% (P = 0.132), respectively. The urinary toxicity of grade 2 and 3 in the chemotherapy group and the control group were 4.2% and 7.1% (P = 0.134) while the grade 2 rectal toxicity were 5.0% and 10.4% (P = 0.317), respectively. No grade 4 toxicity occurred. Considering the chemotherapy-related side effects, grade 3 or above toxicity were leukopenia (41.7%), alopecia (27.1%), thrombocytopenia (2.1%) and edema (2.1%).

CONCLUSION: Results of this interim analysis shows that the addition of adjuvant chemotherapy after standard radical therapy tends to improve the overall recurrence and metastasis free survival of patients with highly malignant prostate cancer, and the adverse effects are tolerable, which should be confirmed by long-term follow-up results.