The introduction of ADCs into frontline ovarian cancer treatment creates a new challenge: conflicting biomarkers. A patient's tumor might be positive for both HER2 (an ADC target) and a BRCA mutation (a PARP inhibitor target), forcing clinicians to choose between two effective targeted therapies without clear guidance.

The treatment landscape for platinum-resistant ovarian cancer has rapidly evolved into a biomarker-driven paradigm. Clinicians must now test for and choose between therapies targeting distinct markers like folate receptor alpha (mirvetuximab), HER2 (T-DXd), and PD-L1 (pembrolizumab), requiring a sophisticated sequencing strategy.

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.

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.

Traditional endpoints like progression-free survival (PFS) incentivize continuous treatment. The NCI group proposes "treatment-free survival," a novel metric that quantifies time spent *off* therapy. This endpoint better captures the patient experience and rewards treatments that provide durable responses after a finite course.

The ADC mirvetuximab is the first drug to demonstrate an overall survival benefit for platinum-resistant ovarian cancer. This groundbreaking result establishes a higher efficacy standard that subsequent therapies will likely need to meet for regulatory approval and clinical adoption, raising the bar for future drug development.

The selection between PARP inhibitors like olaparib and niraparib is not one-size-fits-all. It's a personalized decision based on patient preference for dosing frequency (once vs. twice daily), tolerance for side effects like hypertension, and potential drug-drug interactions.

Historically, therapies for platinum-resistant ovarian cancer were so ineffective that the order of administration was irrelevant. With the advent of multiple active ADCs, the concept of treatment sequencing and potential cross-resistance based on payloads or targets has become a critical, and entirely new, clinical consideration for this disease.