ESTRO 2023

Session Item

Urology

Session Code: 6018

Session Type: Poster (Digital)

Track: Clinical

Outcomes comparison using PSA cut-off values of 0.1 at 6 months in high-risk prostate cancer

Abdenour Nabid, Canada

Presentation Number: PO-1544

Abstract

Abstract Title:

Outcomes comparison using PSA cut-off values of 0.1 at 6 months in high-risk prostate cancer

Authors:

Abdenour Nabid¹, Nathalie Carrier², André-Guy Martin³, Jean-Paul Bahary⁴, Peter Vavassis⁵, Boris Bahoric⁶, Robert Archambault⁷, François Vincent⁸, Redouane Bettahar⁹, Marie Duclos¹⁰, Luis Souhami¹¹

¹Centre hospitalier universitaire de Sherbrooke, Radio-oncologie, Sherbrooke, Canada; ²Centre hospitalier universitaire de Sherbrooke, Biostatistique, Sherbrooke, Canada; ³Centre hospitalier universitaire de Québec, Radio-oncologie, Québec, Canada; ⁴Centre hospitalier universitaire de Montréal, Radio-oncologie, Montréal, Canada; ⁵Hôpital Maisonneuve-Rosemont , Radio-oncologie, Montréal, Canada; ⁶Hôpital Général Juif de Montréal, Radio-oncologie, Montréal, Canada; ⁷Hôpital de Gatineau, Radio-oncologie, Gatineau, Canada; ⁸Centre hospitalier régional de Trois-Rivières, Radio-oncologie, Trois-Rivières, Canada; ⁹Centre de santé et de services sociaux de Rimouski, Radio-oncologie, Rimouski, Canada; ¹⁰McGill University Health Centre, Radiation Oncology, Montréal, Canada; ¹¹McGill University Health Centre, Radiation Oncolgy, Montréal, Canada

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Purpose or Objective

To determine, in patients with high-risk prostate cancer treated with 36 vs. 18 months of androgen deprivation therapy (ADT) and radiotherapy (RT), whether a PSA ≤ 0.1 ng/ml at 6 months after the beginning of ADT, is predictive of a better clinical outcome and to compare those outcomes between 36 and 18 months of ADT.

Material and Methods

We extracted data used from the PCS IV trial in which 630 patients were randomized to ADT of 36 vs. 18 months plus pelvic and prostate RT. We computed outcomes analyses only in patients who completed 18 or 36 months of ADT. Biochemical failure (BF), distant metastases (DM) and prostate cancer-specific mortality (PCSM) were analyzed with competing risks methods and overall survival (OS) and distant metastases-free survival (DMFS) rates with the Kaplan Meier method and the log-rank test. We examined the impact of PSA ≤ 0.1 at 6 months on outcomes.

Results

Results are reported with a median follow-up of 15.2 (IQR 13.2-18.8) years. 480/630 patients were available for the analyses. Of these, 43.8% (210) achieved a PSA ≤ 0.1 at 6 months Overall, patients with a PSA >0.1 at 6 months (56.2%) had significantly more BF (HRs (95% CI) = 2.44 (1.71-3.50), p<0.001), DM (HRs = 2.78 (1.57-4.92), p<0.001), and PCSM (HRs = 2.33 (1.30-4.17), p=0.005) than those with PSA ≤0.1. No difference was seen in OS and DMFS.

In patients receiving 36 months of ADT (167/310), 44.3% (74/167) achieved a nadir of ≤ 0.1 at 6 months compared to 43.4% (136/313) of the 97.8% (313/320) receiving 18 months.

Among patients achieving a PSA ≤0.1 at 6 months, no significant differences were seen between ADT of 36 vs 18 months in all outcomes measured. In patients with PSA > 0.1 at 6 months those receiving 18 months of ADT, compared to 36 months, developed higher rates of BF [46.3% vs. 26.9%, HRs = 2.02 (1.30-3.14), p=0.002] and DM [22% vs. 11.8%, HRs = 1.93 (0.99-3.75), p=0.054]. No significant difference was observed in PCSM, OS and DMFS between groups.

Conclusion

These data suggest that in high-risk patients achieving a PSA nadir ≤ 0.1 at 6 months, 18 months of ADT appears sufficient. Patients remaining with a higher PSA after 6 months of ADT may harbor a more aggressive genetic phenotype and should be considered for trials testing newer therapeutic strategies.