Advances like immunotherapy and Antibody-Drug Conjugates (ADCs) in early-stage Triple-Negative Breast Cancer (TNBC) are so effective that fewer patients are relapsing. This success paradoxically makes it harder to enroll patients in trials for metastatic disease, shifting the trial population toward those with de novo metastatic cancer.

In the Keynote 522 trial for early-stage TNBC, adding pembrolizumab to chemotherapy resulted in only a modest improvement in pathological complete response (pCR). Surprisingly, this small initial gain translated into much more robust and significant long-term improvements in event-free and overall survival.

Clinicians lack evidence to guide treatment for triple-negative breast cancer that relapses shortly after neoadjuvant chemo-immunotherapy. Pivotal trials for new ADCs like Dato-DXD included very few patients with prior immunotherapy, creating a significant and common evidence gap in clinical practice.

Patients with triple-negative breast cancer (TNBC) who recur after standard neoadjuvant chemo-immunotherapy (per the KEYNOTE-522 trial) represent a new, challenging population. There is virtually no clinical data to guide treatment, particularly on whether re-challenging with immunotherapy alongside an ADC is effective.

As CDK4/6 inhibitors move into the adjuvant setting, a new, unstudied patient population is emerging: those who relapse after receiving this combination early. Current metastatic trial data does not apply to these patients, creating a clinical evidence gap and forcing oncologists to extrapolate treatment decisions until new, dedicated studies are completed.

In pivotal ADC trials like ASCENT-03 and 04, over 80% of patients in the control (chemotherapy) arm received the ADC upon progression. This high crossover rate makes interpreting overall survival (OS) data difficult, as the control group's outcomes are artificially improved by subsequent access to the novel drug.

For frail, elderly, or low-tumor-burden patients with early-stage TNBC, single-agent ADCs in the neoadjuvant setting are being explored to de-escalate treatment, potentially sparing them the harsh toxicities of standard multi-agent chemotherapy regimens like KEYNOTE-522.

Unlike ASCENT-03, which required a six-month treatment-free interval, the TROPION-Breast02 trial for datopotamab deruxtecan included patients with immediate relapse after prior therapy. This provides crucial evidence for treating a high-need population with a very poor prognosis, a group often excluded from pivotal trials.

A significant criticism of the pivotal KEYNOTE-564 trial is that only half the patients in the control arm received standard-of-care immunotherapy upon relapse. This lack of subsequent optimal treatment complicates the interpretation of the overall survival benefit, raising questions about its true magnitude.