After observing deep, MRD-negative responses at their starting dose, Colonia Therapeutics unconventionally tested a lower dose level. This counter-intuitive strategy aims to identify the minimum effective dose, which is crucial for maximizing the safety profile (the therapeutic window) and improving commercial viability through lower manufacturing costs.

An ADC may show better response rates than chemotherapy, but its true benefit is compromised if toxicities lead to treatment discontinuation. As seen with failed PARP/IO combinations, if patients cannot tolerate a drug long enough, the regimen's overall effectiveness can become inferior to standard therapy.

A critical reason patients stop ADC treatments is the burden of side effects like skin toxicity or GI issues, not just disease progression. This underscores the urgent need to develop ADCs with better safety profiles, enabling patients to stay on effective therapy longer.

The SURE-01 trial experienced two early deaths, leading to mandatory dose reductions and growth factor support. While this made the ADC sacituzumab govitecan more manageable, it highlights its narrow therapeutic window and the critical need for proactive toxicity management protocols from the outset.

In the REJOYCE ovarian-1 trial for RDXD, the 5.6 mg/kg dose was selected to move forward over a 6.4 mg/kg dose that showed a higher response rate (57%). The lower dose had significantly fewer serious adverse events and a lower rate of interstitial lung disease (ILD), demonstrating a crucial trade-off where safety and tolerability outweigh peak efficacy in late-stage development.

Despite massive unmet need, drug development in higher-risk MDS has stalled because many drugs promising in Phase 1/2 trials fail in Phase 3. Their toxicities, manageable in smaller trials, become prohibitive for the older, co-morbid patient population in larger studies, making a favorable safety profile a critical prerequisite for success.

In the LEAP-010 trial, the combination arm's higher efficacy was offset by significantly greater toxicity (67% vs 38% severe adverse events). This increased treatment burden likely limited sustained therapy and prevented patients from receiving subsequent treatments, ultimately nullifying any survival benefit from improved tumor response.

The REJOICE trial for an ADC in ovarian cancer exemplifies a critical trend: embedding multi-arm dose optimization studies. This approach identified a dose that maintained high response rates (57%) while significantly lowering rates of serious adverse events like ILD (from 6% to 3%), prioritizing patient safety.

Experts believe the stark difference in complete response rates (5% vs 30%) between two major ADC trials is likely due to "noise"—variations in patient populations (e.g., more upper tract disease) and stricter central review criteria, rather than a fundamental difference in the therapies' effectiveness.