What is the effectiveness of mirvetuximab (mirvetuximab soravtansine) for metastatic, folate‑receptor‑α‑positive ovarian cancer that is platinum‑resistant and has received prior systemic therapy?

Mirvetuximab Soravtansine for Platinum-Resistant Ovarian Cancer: Highly Effective First-Line Option

Mirvetuximab soravtansine (MIRV) is highly effective for folate receptor-α (FRα)-positive, platinum-resistant ovarian cancer and should be strongly considered as first-line therapy in this setting, particularly for patients with high FRα expression who have received 1-3 prior systemic therapies.

FDA-Approved Indication and Patient Selection

MIRV is FDA-approved specifically for adult patients with FRα-positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer who have received 1-3 prior systemic treatment regimens 1. Patient selection requires FRα testing using the FDA-approved companion diagnostic VENTANA FOLR1 (FOLR1-2.1) RxDx Assay, with "high" expression defined as ≥75% of tumor cells staining at 2-3+ intensity 1, 2.

Clinical Efficacy: Superior to Standard Chemotherapy

The pivotal MIRASOL trial (Study 0416) demonstrated compelling superiority over investigator's choice chemotherapy in 453 patients with FRα-high, platinum-resistant disease 1:

Key Survival Benefits:

• Progression-free survival (PFS): 5.6 months vs 4.0 months (HR 0.65, p<0.0001)
• Overall survival (OS): 16.5 months vs 12.7 months (HR 0.67, p=0.0046)
• Overall response rate (ORR): 42% vs 16% (p<0.0001)
• Complete response rate: 5% vs 0%

These results represent a 33% reduction in risk of progression and 33% reduction in risk of death compared to standard chemotherapy options (paclitaxel, pegylated liposomal doxorubicin, or topotecan) 1, 3.

Supporting Evidence from SORAYA Trial:

The single-arm SORAYA trial (n=105) confirmed robust activity with:

• ORR: 32.4% in heavily pretreated patients
• Median OS: 15.0 months overall
• 18.7 months OS in patients with 1-2 prior lines vs 11.6 months with 3 prior lines 4, 2

This data strongly supports using MIRV earlier in the treatment sequence rather than reserving it for heavily pretreated patients.

Optimal Treatment Positioning

When to Use MIRV:

1. First-line for platinum-resistant disease: MIRV should be prioritized as the initial treatment when disease becomes platinum-resistant, provided FRα expression is high 4
2. Sequence matters: Post-hoc analysis showed ORR of 34.8% when MIRV was used as first treatment in platinum-resistant setting vs 28.2% when used after other platinum-resistant therapies 4
3. Prior bevacizumab is acceptable: 62% of MIRASOL patients had prior bevacizumab; efficacy was maintained 1
4. Prior PARP inhibitor is acceptable: 55% had prior PARP inhibitor exposure without compromising efficacy 1

Combination Potential:

Emerging data suggests MIRV plus bevacizumab in platinum-resistant disease achieves PFS of 7.66 months and ORR of 42%, representing a promising combination strategy 5, 6.

Safety Profile: Manageable with Monitoring

Critical Safety Considerations:

Ocular Toxicity (Boxed Warning): The most distinctive adverse effect 1:

• Any-grade ocular events: 57% of patients
• Grade ≥3 ocular events: 16%
• Most common: blurred vision (45%), keratopathy (10%), dry eye (4%)
• >90% of ocular events resolved or improved to grade ≤1 3

Required Monitoring Protocol 1:

• Baseline ophthalmic exam (visual acuity + slit lamp)
• Repeat every other cycle for first 8 cycles
• Additional exams as clinically indicated
• Prophylactic artificial tears and topical steroids mandatory

Other Important Toxicities:

• Pneumonitis: Monitor closely; withhold for persistent Grade 2, discontinue for Grade 3-4 1
• Peripheral neuropathy: Dose reduce or hold based on severity 1
• Treatment-related AEs leading to discontinuation: Only 9.2% vs 15.9% with chemotherapy 3

The overall safety profile is superior to standard chemotherapy, with fewer severe adverse events (41.7% vs 54.1%) and lower discontinuation rates 3.

Dosing and Administration

• Standard dose: 6 mg/kg adjusted ideal body weight IV every 3 weeks 1
• Premedication required: Corticosteroid, antihistamine, antipyretic, antiemetic, ophthalmic topical steroids, and lubricating eye drops 1
• Critical: Use 5% Dextrose only; incompatible with normal saline 1
• Continue until disease progression or unacceptable toxicity 1

Practical Implementation Algorithm

For platinum-resistant ovarian cancer patients:

1. Test FRα expression using VENTANA FOLR1 assay
2. If FRα-high (≥75% at 2-3+ intensity):
   • Baseline ophthalmology evaluation
   • Initiate MIRV 6 mg/kg every 3 weeks
   • Consider adding bevacizumab for enhanced response
3. If FRα-low or negative: Follow standard ESMO/NCCN guidelines for platinum-resistant disease (bevacizumab + chemotherapy or single-agent non-platinum options) 7

Critical Caveats

Testing Heterogeneity:

FRα staining can be heterogeneous within tumors, with 15% of cases showing clinically significant scoring changes on re-review 8. Cases scoring 65-85% require careful pathology review, as these borderline cases may be misclassified.

Patient Exclusions:

• Corneal disorders or active ocular conditions requiring treatment
• Grade >1 peripheral neuropathy at baseline
• Non-infectious interstitial lung disease 1

Guideline Context:

While MIRV is not yet incorporated into the 2023 ESMO guidelines 7 or 2024 NCCN guidelines 9 as a standard recommendation (these predate or coincide with full FDA approval), the FDA approval and Level I evidence from MIRASOL establish it as a preferred option for appropriately selected patients.

Bottom Line

Mirvetuximab soravtansine represents a paradigm shift in treating FRα-high platinum-resistant ovarian cancer, offering superior survival, response rates, and tolerability compared to conventional chemotherapy. It should be prioritized early in the platinum-resistant setting rather than reserved as a last-line option. The key is proper patient selection through FRα testing and proactive management of ocular toxicity through mandatory ophthalmologic monitoring and prophylaxis.