Beyond efficacy, new therapies like bispecifics require significant institutional support. Clinicians need training for unfamiliar side effects like CRS, and facilities need resources like observation units and admission protocols, creating a steep implementation curve for clinical practice.
Developers often test novel agents in late-line settings because the control arm is weaker, increasing the statistical chance of success. However, this strategy may doom effective immunotherapies by testing them in biologically hostile, resistant tumors, masking their true potential.
For antibody-drug conjugates (ADCs) to make a meaningful impact in prostate cancer, the clinical development bar is exceptionally high. Merely showing activity in late-line settings is insufficient; the true measure of success is demonstrating superiority over the established chemotherapy standard, docetaxel.
Unlike bladder cancer, prostate cancer has highly effective androgen-pathway inhibitors (ARPIs) that extend survival. This success has pushed chemotherapy and, by extension, ADC development to later treatment lines as clinicians prioritize other novel mechanisms of action first.
The future of advanced prostate cancer treatment may involve combining ADCs with bispecific T-cell engagers. This strategy could use ADCs for a short duration to deliver a potent hit, followed by immunotherapy to achieve durable remission, potentially reducing toxicity and enabling earlier use.
Even when testing drugs in heavily pre-treated patients, clinical trials incorporate subtle biological selection criteria. For instance, the COMPASS trial excludes patients with visceral metastases, a tactic to enrich for a population more likely to respond and avoid the most aggressive disease subtypes.
An antibody-drug conjugate's (ADC) effectiveness is capped by its chemotherapy payload. In prostate cancer, topoisomerase inhibitors have a poor track record. Therefore, ADCs using this payload face an uphill battle compared to those with proven payloads like microtubule inhibitors (taxanes).