The goal of this clinical trial is to evaluate the outcomes of a shorter treatment duration (12 months) with an androgen receptor pathway inhibitor (ARPI), in this study Apalutamide or Enzalutamide, in patients with low-volume, hormone-sensitive metastatic prostate cancer (mCSPC), with the possibility to restart treatment if needed.

The main research question is whether discontinuation of ARPI therapy after 12 months, with the option to restart treatment upon disease progression, is non-inferior to continued ARPI therapy, potentially reducing toxicity and costs.

Eligible patients will be randomized after completing 12 months of ARPI treatment, to one of the following two arms:

1. ADT + continued ARPI (Apalutamide or Enzalutamide)
2. ADT + ARPI discontinued after 12 months, with the option to resume ARPI in case of a confirmed PSA rise. The confirmatory PSA sample must be obtained at least 4 weeks after the initial rise.

This study aims to minimize toxicity associated with prolonged use of ARPIs in patients with low-volume, hormone-sensitive metastatic prostate cancer.

Inclusion Criteria:

• Male and ≥18 years of age
• Capable of understanding and complying with protocol requirements and able to understand and sign the informed consent form
• Histological diagnosis of prostate adenocarcinoma
• Low volume de novo metastatic disease (M1a or M1b) defined as anything other than fitting the criteria for high-volume metastatic disease, e.g., four or more bone lesions with one or more lesions in any body structure beyond the spine or pelvis, or visceral disease (non-nodal). This has been assessed by either bone scan and computed tomography (CT), or PSMA-PET scan. Low-volume disease has subsequently been confirmed by the local (multidisciplinary) team after consideration of the available imaging results as per the standard imaging protocol for the site.
• ADT initiated within 6 weeks prior to inclusion
• Eastern Cooperative Oncology Group (ECOG) performance scale status of 0, 1 or 2
• Fit for treatment with apalutamide or enzalutamide according to treating physician

Exclusion Criteria:

• Pathological finding consistent with small cell, ductal or neuroendocrine carcinoma of the prostate
• Other prior malignancy less than or equal to 5 years prior to randomization except for squamous or basal cell skin carcinoma or non-invasive superficial bladder cancer
• History of seizures or medications known to lower seizure threshold
• Any other prior treatment for prostate cancer other than ADT (e.g., other next generation anti-androgens or other CYP17 inhibitors, chemotherapy, immunotherapy, or radiopharmaceutical agents)
• ADT started more than 6 weeks before inclusion