Relationship between undetectable PSA nadir and outcomes for patients with metastatic hormone-sensitive prostate cancer (mHSPC) in IRONMAN, the International Registry for Men with Advanced Prostate Cancer.
Authors: McManus Hannah Dzimitrowicz , Howard Lauren , Crowell Kerri-Anne , Hyslop Terry , Autio Karen A. , Rathkopf Dana , Dreicer Robert , Chi Kim N. , Ong Michael , Mateo Joaquin , Enting Deborah , Esteban Emilio , Khoo Vincent , McMannis Amanda , Green Rebecca , Pileggi Shannon , Vinson Jake , Kantoff Philip W. , Mucci Lorelei A , George Daniel J. 
Published: February 2025

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Background:
Intensified androgen deprivation therapy (ADT) with an androgen receptor pathway inhibitor (ARPI) and/or docetaxel has led to improved outcomes for metastatic hormone-sensitive prostate cancer (mHSPC) in multiple clinical trials. Achievement of an undetectable PSA nadir has been associated with improved clinical outcomes, but real-world data across treatment regimens are limited.
Methods:
We evaluated PSA response and outcomes for patients with mHSPC treated with ADT monotherapy (mono), ADT + ARPI, and ADT + docetaxel in the International Registry for Men with Advanced Prostate Cancer (IRONMAN). All patients with mHSPC enrolled in IRONMAN between 2017 and August 2023 in the United States, Canada, Spain, and England were included. Patients treated with triplet therapy were excluded due to small numbers. Undetectable PSA nadir, defined as PSA <0.2 ng/mL, was evaluated at 6 and 12 months after treatment start. In this real-world study, relapse was defined as meeting one of the following criteria: PSA progression (≥25% PSA increase from nadir and absolute increase >2 ng/mL), treatment change preceded by new metastasis location, or change to a neuroendocrine prostate cancer regimen. Rates of relapse were calculated using Kaplan Meier estimates, with confidence intervals based on standard errors calculated using the Greenwood formula.
Results:
Among 1,377 eligible patients, treatment was most commonly ADT + ARPI (n=775) followed by ADT mono (n=375) and ADT + docetaxel (n=227). In the overall population, PSA nadir <0.2 ng/mL was achieved in 40% (n=554) at 6 months and 51% (n=702) at 12 months. Rates of PSA nadir <0.2 ng/mL at 6 months were: 51% for ADT + ARPI, 27% for ADT mono, and 26% for ADT + docetaxel. At 12 months, rates of PSA nadir <0.2 ng/mL increased to: 63% for ADT + ARPI, 38% for ADT mono, and 32% for ADT + docetaxel. During a median follow-up of 18 months, 291 patients (21%) experienced disease relapse; 19% experienced PSA progression. The percentage of patients in each treatment group with disease relapse at months 12, 24, and 36 of treatment are shown (Table); treatment groups are divided by whether patients had achieved PSA nadir <0.2 ng/mL in 6 months.
Conclusions:
In this non-randomized, real-world registry, patients with mHSPC who achieved a PSA nadir <0.2 ng/mL had a lower relapse rate than patients who did not, regardless of treatment.

Percentage (95% CI), [number at risk] of patients with relapse at timepoint.

Treatment
Month 6
Month 12
Month 24
Month 36

ADT Monotherapyn=375
PSA <0.2 ng/mL
0%(0, 0)[60]
1.7%(0, 5.0)[31]
11%(0, 24)[15]

PSA ≥0.2 ng/mL
18%(11, 24)[80]
41%(30, 51)[38]
45%(33, 55)[19]

ADT + ARPIn=775
PSA <0.2 ng/mL
2.2%(0.6, 3.8)[288]
9.7%(5.9, 13)[166]
18%(12, 24)[76]

PSA ≥0.2 ng/mL
21%(16, 26)[178]
42%(35, 49)[81]
50%(42, 58)[37]

ADT + Docetaxeln=227
PSA <0.2 ng/mL
8.2%(0.2, 16)[44]
22%(8.9, 33)[29]
36%(18, 50)[14]

PSA ≥0.2 ng/mL
34%(25, 43)[69]
62%(50, 72)[21]
73%(59, 82)[12]