A dramatic epidemiological shift has occurred in HER2+ breast cancer. Due to highly effective adjuvant therapies preventing recurrence, the majority of new metastatic cases (two-thirds) are now de novo, a complete reversal from 15 years ago when relapsed disease dominated.

Cancers with estrogen receptor (ER) expression of 50% or less, while technically HR+, often behave biologically like basal or triple-negative tumors. These cancers are not primarily endocrine-driven and show a significant benefit from the addition of immune checkpoint inhibitors, challenging traditional subtype classifications.

Achieving a pathologic complete response (path CR) in the bladder after neoadjuvant therapy is a marker of drug efficacy, not a signal to stop treatment. Because patients die from metastatic, not local, disease, a path CR should be seen as a reason to "double down" on the effective systemic therapy to eradicate micrometastases.

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.

The trial's 57.1% pathologic complete response (pCR) rate is deceptively conservative. It categorized patients who responded well but declined surgery as non-responders, suggesting the treatment's true biological efficacy is even higher than the already impressive reported figure.

In neoadjuvant therapy, a patient's long-term outcome is better predicted by stopping tumor DNA shedding (ctDNA clearance) than by achieving pathologic complete response (pCR), the traditional gold standard. This redefines what constitutes a successful treatment response before surgery.

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.

Clinical trials use arbitrary, time-based definitions (e.g., relapse within 2 years) for endocrine resistance. This isn't a perfect biological classification but a practical necessity to create homogeneous patient groups for testing, which may not fully reflect the diverse patient population in clinical practice.

Unlike immunotherapy, neoadjuvant osimertinib yields poor pathologic complete response (pCR) rates. However, it significantly improves major pathologic response (MPR) and survival, suggesting pCR may be the wrong efficacy endpoint for cytostatic EGFR TKIs, which have a different mechanism of action than immunotherapy.