The effectiveness of radioligand therapy is counterintuitive: as tumors shrink and PSMA binding sites decrease, less radiation is delivered to the cancer. The VISION trial showed the first two doses delivered more radiation to the tumor than the subsequent four, questioning the value of a fixed, prolonged treatment schedule.

The next innovation for PARP inhibitors will likely involve combinations with other DNA-damaging agents beyond just ARPIs. Promising partners include radioligands like radium (an alpha emitter) and lutetium, or even therapies like superphysiologic testosterone (BAT) that are theorized to work by inducing DNA breaks.

The LUNAR trial's positive outcome was unexpected. Patients received SBRT for all PET-visible lesions, meaning the added Lutetium-PSMA was targeting disease that couldn't be seen. This implies the radioligand can effectively bind to and treat microscopic cancer cells, challenging the notion it only works on clearly imaged tumors.

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.

Lutetium faces criticism for its fixed 6-cycle regimen, which may be suboptimal as the PSMA target diminishes with ADT. However, this critique is rarely applied to other drugs like PARP inhibitors, which are given until progression. This highlights a double standard and the tension between using a fixed regimen for regulatory approval versus finding the optimal dose in practice.

The development of PARP-1 selective inhibitors like seriparib signals a shift in drug innovation. Instead of only chasing higher efficacy, these new agents aim for a more favorable toxicity profile (less GI toxicity, fewer dose discontinuations) to improve patient quality of life and treatment adherence.

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.

Instead of administering all six planned doses of PSMA Lutetium upfront in the hormone-sensitive setting, a novel "sandwich" strategy is being considered. This involves giving a few doses, re-imaging, and reserving subsequent doses for later, potentially optimizing efficacy and managing long-term toxicity.

While Lutetium shows promise in hormone-sensitive prostate cancer, experts raise concerns about potential late-effect toxicities for patients surviving many years. This contrasts with docetaxel, where toxicity is acute and resolves after treatment, highlighting an unknown long-term risk-benefit profile for new radioligand therapies.