Unlike chemotherapy, the effectiveness of radioligand therapy (e.g., Pluvicto) wanes as it succeeds. Successful treatment reduces the PSMA target, meaning less radiation is delivered to the cancer and more to healthy organs. This physics-based reality underpins the concept of adaptive dosing.
A surprising number of physicians have already accepted the concept of adaptive radioligand dosing, stopping treatment in high-responding patients. This acceptance is driven by the compelling physics of diminishing returns, even though robust clinical trial data to guide this practice does not yet exist.
In advanced prostate cancer with few options, clinicians retreat patients with radioligand therapy after an initial response, despite a lack of formal data. The rationale is practical: for a patient who previously responded well and has no better alternatives, reusing an effective therapy is a logical clinical decision.
The CCTG PR21 trial revealed a paradox: while Lutetium achieved a much higher PSA response rate than docetaxel chemotherapy, overall survival was better for patients who received docetaxel first. This counter-intuitive finding complicates treatment sequencing and challenges the assumption that higher initial response equals better long-term outcomes.
Despite showing a strong overall survival (OS) advantage in trials, Radium-223 is not widely used. It is considered a "mystery box" because it rarely produces satisfying intermediate results like PSA declines or cleared scans. This parallels adoption challenges faced by other therapies with proven OS but weak surrogate endpoints.
Recognizing that radioligand therapy is most effective early when tumors are "target-rich," new clinical trials accelerate dosing and intensity upfront. This strategy aims to deliver the most significant therapeutic blow before diminishing returns set in as the tumor responds and the target is lost.
Even within a single patient, tumor lesions exhibit significant heterogeneity in PSMA expression, with some being "hot" and others "not." This ensures that a standard dose of radioligand therapy will not be delivered uniformly across all disease sites, creating an inherent mechanism for resistance and incomplete response.