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.

Trastuzumab deruxtecan (TDXD) and datopotamab deruxtecan (Dato-DXd) share the same cytotoxic payload, yet Dato-DXd has a much lower rate of interstitial lung disease (ILD). This indicates the toxicity is driven by the antibody-antigen interaction, not the payload itself.

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.

While a small risk of fatal toxicity like interstitial lung disease (ILD) from T-DXd is often accepted in metastatic disease, it's a major concern in the early-stage, curative setting. The ethical bar for safety is much higher when the goal is to cure, making oncologists more cautious about adoption despite efficacy.

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.

The risk of serious interstitial lung disease (ILD) with the drug TDXD is heavily dependent on the total duration of therapy. A short, 4-cycle neoadjuvant course has a low 4% ILD rate, whereas a longer 14-cycle adjuvant course sees this risk more than double to over 10%, making the shorter pre-surgical approach significantly safer.

In the DESTINY-CRC02 trial, the lower 5.4 mg/kg dose of trastuzumab deruxtecan (TDXD) resulted in a higher response rate in colorectal cancer compared to the 6.4 mg/kg dose used in gastric cancer. This counter-intuitive finding suggests better tolerability led to longer treatment duration and superior outcomes.

Despite being advanced targeted therapies, TROP2-directed ADCs present complex safety profiles. Oncologists must manage classic chemotherapy side effects like nausea and cytopenias alongside unique, serious toxicities including stomatitis, ocular issues, and potentially fatal interstitial lung disease, requiring specialized patient monitoring and counseling.