While platinum chemotherapy is considered the standard treatment after a patient progresses on a first-line ADC-IO combination, experts admit this is a standard "based on nothing." There is no clinical trial data to prove its efficacy in this specific setting; it serves only as a placeholder for new clinical trials.

The Destiny Breast 11 trial compared a new drug to a chemotherapy regimen (ACTHP) that many US oncologists no longer use. This choice of a less common control arm makes it difficult for them to directly compare the new treatment's efficacy against their own current standard (TCHP), complicating adoption.

Positive data from both DESTINY-Breast09 (TDXD-based) and PATINA (CDK4/6i maintenance) create a new dilemma. With similar PFS outcomes, the first-line choice for metastatic HER2+/HR+ patients now hinges on toxicity profiles and patient preference rather than a single efficacy winner.

Even within recent major clinical trials like HER2CLIMB-05, less than half of eligible hormone receptor-positive patients received endocrine therapy. This highlights a critical and widespread gap in clinical practice, as this treatment adds significant benefit.

Unlike other PARP inhibitor trials that used a less effective second-line hormonal agent as a comparator, the TRITON 3 study tested Rucaparib against a physician's choice that was predominantly docetaxel chemotherapy. This robust design against a true standard of care makes its positive outcome more clinically significant.

The DESTINY-Breast11 trial showed a neoadjuvant regimen of TDXD followed by THP achieved a 67.3% pathologic complete response (pCR) rate in high-risk HER2+ breast cancer. This is the highest pCR rate seen in a registrational trial, signaling a potential new standard of care.

A subtle finding in the DESTINY-Breast11 trial, where TDXD alone underperformed TDXD followed by THP, suggests that taxane-based chemotherapy might remain effective even after a patient's HER2-positive cancer becomes resistant to the antibody-drug conjugate TDXD.

To mitigate long-term toxicity from TDXD, oncologists are proposing an "induction/maintenance" approach. Patients receive TDXD for an initial period to achieve maximal response, then switch to a less toxic maintenance regimen for a "chemotherapy holiday," improving quality of life.

The TRILINX trial revealed Xevinapant's toxicity was so high that it forced reductions in standard, effective treatments like cisplatin and radiation. This compromised the foundational therapy, leading to worse patient outcomes and demonstrating a key risk in adding novel agents to established regimens.