In ovarian cancer trials, many patients in the placebo group later receive a PARP inhibitor. This crossover "pollutes" the data, making it difficult to prove a statistically significant overall survival benefit for frontline PARP maintenance, despite its clear effectiveness.

The traditional six-month timeframe for defining platinum sensitivity is being challenged. A growing theory suggests that tumors progressing while on a PARP inhibitor have a distinct biology that responds poorly to subsequent platinum, indicating a potential need to move directly to therapies like ADCs.

The traditional practice of classifying recurrent ovarian cancer as 'platinum-sensitive' or 'platinum-resistant' based on a six-month treatment-free interval is rapidly becoming obsolete. The introduction of maintenance therapies like PARP inhibitors is changing tumor biology and response patterns, suggesting this simple time-based distinction no longer adequately reflects the clinical reality.

Real-world data shows that in platinum-sensitive ovarian cancer patients who have progressed on PARP inhibitors, subsequent platinum-based chemotherapy has a surprisingly low response rate of only 20%. This quantifies a significant opportunity for highly active ADCs to potentially replace platinum in this growing patient population.

The widespread use of PARP inhibitors has altered tumor biology in platinum-sensitive ovarian cancer. A recent meta-analysis of heavily pretreated patients, 97% of whom had prior PARP inhibitor exposure, revealed an objective response rate to subsequent therapy of only 17%—far lower than historical expectations, highlighting a critical unmet clinical need.

The modest benefit of PARP inhibitors in metastatic breast cancer, compared to ovarian cancer, is likely due to resistance induced by prior exposure to DNA-damaging agents like anthracyclines. This explains the clinical rationale for moving PARP inhibitors to earlier treatment settings, such as neoadjuvant or adjuvant therapy, before resistance develops.

The EV302 trial update established a new, robust benchmark for second-line therapy. Platinum chemotherapy after EV/Pembrolizumab progression showed only a 21% response rate, which is lower than prior retrospective estimates and highlights the need for better sequencing options.

For HRD-positive ovarian cancer, a strong initial response to platinum chemotherapy may justify using a PARP inhibitor alone for maintenance. A weaker response, however, suggests adding bevacizumab for a potentially greater benefit, using clinical response as a key decision-making tool.

The initial broad enthusiasm for PARP inhibitors in ovarian cancer has been refined. New data confirms a lack of overall survival improvement for patients with HRD-negative (or HR proficient) tumors, pushing clinicians toward a precision medicine approach where these drugs are reserved for patients with BRCA mutations or HRD-positive disease who are most likely to benefit.