ELAHERE® Shows Overall and Progression-Free Survival Benefit Regardless of Prior PARPi Exposure or Prior Lines of Therapy in FRα-Positive Platinum-Resistant Ovarian Cancer

ELAHERE^® Shows Overall and Progression-Free Survival Benefit Regardless of Prior PARPi Exposure or Prior Lines of Therapy in FRα-Positive Platinum-Resistant Ovarian Cancer

Data Further Position ELAHERE to Become the New Standard of Care for Patients with FRα-Positive Platinum-Resistant Ovarian Cancer

Findings to be Highlighted in Oral Presentation at ESGO Annual Congress

Waltham, MA – September 28, 2023 – ImmunoGen Inc. (Nasdaq: IMGN), a leader in the expanding field of antibody-drug conjugates (ADCs) for the treatment of cancer, today announced findings from two subset analyses of the Phase 3 confirmatory MIRASOL trial (GOG 3045/ENGOT OV-55) evaluating the safety and efficacy of ELAHERE^® (mirvetuximab soravtansine-gynx) compared to chemotherapy in patients with folate receptor alpha (FRα)-positive platinum-resistant ovarian cancer (PROC). The findings will be presented by Dr. Toon Van Gorp in an oral presentation today at the 24th Congress of the European Society of Gynaecological Oncology (ESGO) in Istanbul, Turkey.

“Consistent with the strong topline MIRASOL data where superiority was seen across all efficacy endpoints, these subset analyses show that the improvements in progression-free survival, objective response rates, and overall survival demonstrated in the overall study population are also observed regardless of the number of prior lines of therapy,” said Toon Van Gorp, Professor of Gynaecological Oncology at the University of Leuven. “Importantly, the benefit seen with ELAHERE in patients treated with a prior PARP inhibitor is particularly encouraging, as it has been shown that PARP inhibitors have a potential negative impact on the efficacy of subsequent chemotherapies. These new data being presented at ESGO, including a consistent safety and tolerability profile, provide valuable insights for physicians into ELAHERE’s broad and meaningful benefit compared to chemotherapy and further position ELAHERE to become the new standard of care for patients with FRα-positive PROC.”

MIRASOL is a randomized Phase 3 trial of ELAHERE versus investigator's choice (IC) of single-agent chemotherapy (weekly paclitaxel, pegylated liposomal doxorubicin (PLD), or topotecan). MIRASOL enrolled 453 patients with PROC, whose tumors express high levels of FRα using what is now the Ventana FOLR1-2.1 assay, and who have been treated with one to three prior regimens. Patients were stratified by number of prior lines of therapy (14% had one prior line of therapy, 40% had two prior lines of therapy, and 46% had three prior lines of therapy) and by IC chemotherapy, with paclitaxel as the most commonly chosen (41%), followed by PLD (36%) and topotecan (23%). 62% of patients received prior bevacizumab; 55% received a prior PARP inhibitor. The primary endpoint of this trial is progression-free survival (PFS) by investigator assessment. Key secondary endpoints include objective response rate (ORR), overall survival (OS), and patient-reported outcomes (PROs).

EFFICACY OF MIRVETUXIMAB SORAVTANSINE IN FOLATE RECEPTOR ALPHA HIGH, PLATINUM-RESISTANT OVARIAN CANCER BY TYPE AND NUMBER OF PRIOR TREATMENT REGIMENS: AN EXPLORATORY ANALYSIS

Lead Author: Toon Van Gorp, MD
Date/Time: Thursday, September 28, 2023, 2:00-2:35pm TRT / 7:00-7:35am ET
Abstract: #1015 and #1056

In addition to the top-line MIRASOL data previously disclosed and subsequently presented at the 2023 American Society of Clinical Oncology (ASCO) Annual Meeting, the following new data are being presented at ESGO:

• ELAHERE demonstrated clinically meaningful improvement in PFS and ORR by investigator assessment and in OS compared to IC chemotherapy, regardless of prior PARPi exposure.
• In patients with prior PARPi (n=251), PFS hazard ratio (HR) was 0.58 (95% CI: 0.43, 0.78; p= 0.0002); in the PARPi-naïve subset (n=191), PFS HR was 0.74 (95% CI: 0.54, 1.03, p =0.0685).
• In patients with prior PARPi, ORR in the ELAHERE arm was 45% (95% CI: 36%, 54%), including 7 CRs, compared to 17% (95% CI: 11%, 25%), with no CRs, in the IC chemotherapy arm (p<0.0001); in the PARPi-naïve subset, ORR in the ELAHERE arm was 40% (95% CI: 30%, 51%), including 5 CRs, compared to 14% (95% CI: 8%, 23%), with no CRs, in the IC chemotherapy arm (p<0.0001).
• In patients with prior PARPi, OS HR was 0.48 (95% CI: 0.33, 0.71; p= 0.0002); in the PARPi-naïve subset, OS HR was 0.90 (95% CI: 0.590, 1.38, p =0.6319).
• ELAHERE demonstrated clinically meaningful improvements in PFS and ORR by investigator assessment and in OS compared to IC chemotherapy, regardless of prior lines of therapy (PLOT).
• In patients with 1 or 2 PLOT (n=245), the PFS HR was 0.61 (95% CI: 0.45, 0.81; p=0.0007); in patients with 3 PLOT (n=208), PFS HR was 0.71 (95% CI: 0.52, 0.98; p=0.0362).
• In patients with 1 or 2 PLOT, ORR in the ELAHERE arm was 46% (95% CI: 37%, 55%), including 10 complete responses (CRs), compared to 15% (95% CI: 9%, 22%), with no CRs, in the IC chemotherapy arm (p<0.0001); in patients with 3 PLOT, ORR in the ELAHERE arm was 38% (95% CI: 29%, 48%), including 2 CRs, compared to 18% (95% CI:11%, 26%), with no CRs, in the IC chemotherapy arm (p=0.0009).
• In patients with 1 or 2 PLOT, OS HR was 0.66 (95% CI: 0.45, 0.98; p=0.0375); in patients with 3 PLOT, OS HR was 0.65 (95% CI: 0.43, 0.96; p=0.0308).
• ELAHERE demonstrated a tolerable safety profile compared to IC chemotherapy consisting predominantly of low-grade ocular and gastrointestinal events.
• In all patients, the frequency of grade 3+ treatment-emergent adverse events (TEAEs) was 42% with ELAHERE and 54% with IC chemotherapy; the frequency of serious adverse events (SAEs) was 24% with ELAHERE and 33% with IC chemotherapy; and the frequency of discontinuations due to a TEAE was 9% with ELAHERE and 16% with IC chemotherapy.

"Given ELAHERE is a potentially transformative option for those with platinum-resistant ovarian cancer, it will be important for clinicians to understand the consistency across these subset analyses from MIRASOL as they make treatment decisions with their patients," said Michael Vasconcelles, MD, ImmunoGen's Executive Vice President, Research, Development, and Medical Affairs. "Looking forward, we are excited to submit our MAA and sBLA to the EMA and FDA, respectively, before year end while continuing to advance our broader development program as we prioritize delivering ELAHERE to eligible patients in need."

In November 2022, the US Food and Drug Administration (FDA) granted accelerated approval for ELAHERE for the treatment of adult patients with FRα-positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer who have received one to three prior systemic treatment regimens based on ORR and duration of response data from the pivotal SORAYA trial.

Additional information can be found at www.congress.esgo.org.