When PSMA PET became the standard of care for detecting prostate cancer metastasis, the PROTEUS trial amended its protocol to include it alongside conventional imaging. The trial's positive Metastasis-Free Survival (MFS) result was driven by this composite endpoint, as the analysis using conventional imaging alone was not statistically significant.

Standard RECIST criteria can misclassify a significant response as "stable disease." A desmoid tumor can shrink dramatically in volume (from a "softball" to a "pencil") but maintain its length, showing no change by RECIST. This suggests clinicians are likely underestimating the true benefit of therapies.

Data from trials like Niagara suggests a powerful new paradigm for assessing treatment success. Combining urine tumor DNA (uTDNA) for local disease and circulating tumor DNA (ctDNA) for systemic relapse offers a more dynamic view than traditional pathology and is poised to become the superior surrogate endpoint in bladder cancer trials.

In metastatic hormone-sensitive prostate cancer, many patients receive multiple subsequent therapies, making Overall Survival (OS) a difficult endpoint to achieve. Therefore, a large, meaningful improvement in radiographic progression-free survival (RPFS) is considered a critical and actionable outcome for patients.

Traditional endpoints like progression-free survival (PFS) incentivize continuous treatment. The NCI group proposes "treatment-free survival," a novel metric that quantifies time spent *off* therapy. This endpoint better captures the patient experience and rewards treatments that provide durable responses after a finite course.

In the SUNRISE 2 trial, 44% of patients had no detectable tumor after pre-treatment resection. This high baseline inflates the final clinical complete response (CR) rates (e.g., 59% in the control arm), making CR a misleading indicator of the actual therapeutic benefit, which was a much smaller improvement over baseline.

Experts believe molecular tests like Decipher and PTEN status are superior to simply counting bone lesions for guiding treatment. While not yet standard practice for all decisions, this represents a significant shift towards using underlying tumor biology to determine therapy, like adding docetaxel.

In metastatic hormone-sensitive prostate cancer (mHSPC), radiographic progression-free survival (rPFS) is no longer seen as a convincing primary endpoint on its own. Clinicians demand a clear signal for overall survival (OS) improvement, citing historical data where early treatment intensification showed significant OS gains.

While depth of response strongly predicts survival for an individual patient, the FDA analysis concludes it cannot yet be used as a surrogate endpoint to replace overall survival in pivotal clinical trials. It serves as a measure of drug activity, similar to response rate, but is not sufficient for drug approval on its own.