PSMA expression is not a static marker but a dynamic stress response. Cancer cells increase PSMA expression when stressed by treatments like androgen receptor blockade or radiation. This model frames PSMA as a survival mechanism for the cell, explaining its association with more aggressive disease.

Early data shows that combining PARP inhibitors with radioligand therapy like lutetium-PSMA is surprisingly safe, unlike toxic combinations with chemotherapy. This promising strategy may potentiate the DNA-damaging effect of the beta-emitting radiopharmaceutical, potentially extending its benefit to a broader patient population beyond those with HR-deficient tumors.

The PSMA Addition study, adding lutetium in metastatic hormone-sensitive prostate cancer, showed an RPFS benefit. However, initial data suggested adverse quality of life scores. Upcoming results on pain and skeletal events are critical to determine if the toxicity profile undermines its clinical utility in this earlier disease setting.

The EMBARK trial showed that enzalutamide monotherapy was superior to standard ADT monotherapy for metastasis-free survival. This suggests potent AR antagonism may be a more effective strategy than simply depleting the testosterone ligand, challenging the long-held dogma of ADT being the fundamental building block for systemic prostate cancer therapy.

Early in treatment, tumors are "target-rich" with high PSMA expression, creating an ideal window for radioligand therapy. Citing data from the VISION trial, new clinical trials are being designed to accelerate dosing and intensity upfront to maximize impact, then de-escalate as the target diminishes.

The primary benefit of combining an androgen receptor inhibitor with lutetium-PSMA is a complementary, additive effect. The drugs target different cancer cell populations: the AR-inhibitor targets low-PSMA disease, while lutetium targets high-PSMA disease. This is more significant than any minor synergistic effect from PSMA upregulation.

PSMA-PET imaging at baseline can identify who benefits from adding lutetium-PSMA. In the ENZA-P trial, patients with high-volume disease saw a significant survival benefit from the combination. Conversely, those with low-volume disease derived no benefit, suggesting imaging can be used for patient selection.

If lutetium-PSMA is approved and used upfront in hormone-sensitive disease, clinicians may become more comfortable with radioligands generally. This could lead them to use the enzalutamide-radium combination more frequently later on, paradoxically increasing radium's use by flipping the current treatment sequence.

Even when an ARPI is no longer effective as a standalone therapy, continuing it may be beneficial. By maintaining pressure on the androgen receptor pathway, the drug can upregulate downstream targets like PSMA, potentially enhancing the efficacy of subsequent PSMA-targeted therapies like radioligands or ADCs.