Treatment Response To ImmunoGen’s Mirvetuximab Soravtansine Found To Be Substantially Greater In Ovarian Cancer With High Expression Of Folate Receptor Alpha

WALTHAM, Mass.--(BUSINESS WIRE)--ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops targeted anticancer therapeutics using its antibody-drug conjugate (ADC) technology, today reported findings with mirvetuximab soravtansine, its novel folate receptor alpha (FRa)-targeting ADC product candidate, being presented at the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics (abstract #C47). Analysis of the association between the amount of FRa present on patient cancer cells and response to treatment with mirvetuximab soravtansine found nine of ten (90%) patients with high levels of FRa had an objective response on treatment.

“These early findings are highly encouraging as they underscore the potential of mirvetuximab soravtansine to make an important difference for patients with ovarian cancer”

“These early findings are highly encouraging as they underscore the potential of mirvetuximab soravtansine to make an important difference for patients with ovarian cancer,” said Dr. Charles Morris, chief development officer. “The data are from patients with heavily pretreated platinum-resistant ovarian cancer, which is a difficult disease to treat. We will be assessing mirvetuximab soravtansine as single-agent therapy for patients with pretreated FRa-positive ovarian cancer in our FORWARD I trial, a study we intend to use for registration purposes.”

The findings presented today are from an analysis of 20 efficacy-evaluable patients with platinum-resistant ovarian cancer who received mirvetuximab soravtansine in Phase 1 testing at its selected dose. Patients were categorized as having high, medium or low amounts of FRa on their cancer cells.¹ Enrollment criteria for the clinical study required all patients to have at least low expression.

• Nine of the ten patients with high FRa expression had an objective response (2 complete responses/CRs, 7 partial responses/PRs by RECIST 1.1 criteria). Six of these responders remained on treatment for at least 24 weeks.
• The six patients with medium expression all had tumor regression. One patient had an objective response (unconfirmed PR) and one had tumor shrinkage with new lesion formation (mixed response/MR). An additional patient remained on treatment for more than six months but did not have an objective response.
• Four patients had low expression and none had an objective response. One patient was still on treatment at the time of data cut off for presentation.

The ORR was 50% for all 20 efficacy-evaluable patients. Among all 22 patients evaluable for tolerability, the majority of adverse events reported were low grade (grade 1 or 2), with diarrhea, blurred vision, vomiting, fatigue, and nausea the most common treatment-emergent events reported (>30% of patients).

ImmunoGen anticipates reporting mature data from the full 46-patient cohort in this study at a medical meeting in 2016.

The FORWARD I Trial

ImmunoGen’s FORWARD I trial will assess mirvetuximab soravtansine as single-agent therapy for the treatment of ovarian cancer previously treated with three to four prior regimens. Patients will have medium or high expression of FRa to qualify for enrollment in this Phase 2 study. Patient enrollment is expected to start in late 2015.

About Mirvetuximab Soravtansine

Mirvetuximab soravtansine (IMGN853) is a FRa-targeting ADC developed and wholly owned by ImmunoGen. It comprises a FRa-binding antibody conjugated to DM4, a potent cancer-killing agent created by ImmunoGen for use in ADCs. The antibody serves to target the DM4 specifically to FRa-positive cancer cells which the DM4 can then kill. FRa is highly expressed on many cases of epithelial ovarian cancer.² It also is highly expressed on other types of solid tumors including endometrial cancer and some non-small cell lung cancers.

About Ovarian Cancer

Each year, there are approximately 21,300 new cases of ovarian cancer diagnosed in the US and more than 14,200 women die from the disease.³ Once the cancer has been treated with several lines of combination regimens, patients may be treated with single-agent therapy, which typically have response rates around 15-20%.⁴

About ImmunoGen, Inc.

ImmunoGen is a clinical-stage biotechnology company that develops targeted anticancer therapeutics using its proprietary ADC technology. The Company's lead wholly owned product candidate, mirvetuximab soravtansine, is a potential treatment for FRa-positive ovarian cancers and other solid tumors. Major healthcare companies have licensed rights to use ImmunoGen's technology to develop novel anticancer therapies; Roche's marketed product, Kadcyla^®, utilizes ImmunoGen's ADC technology. More information about the Company can be found at www.immunogen.com.

¹High, medium, low: >75%, 50-74%, and 25-49%, respectively, of tumor cells have strong (3+) or moderate (2+) expression of FRa, as assessed by immunohistochemistry (IHC), a standard method of target measurement for antibody-based therapeutics.

²AACR 2015 abstract #3400A.

³American Cancer Society (2015), Cancer Facts & Figures.

⁴From prescribing information and published clinical data.

Kadcyla^® is a registered trademark of Genentech, a member of the Roche Group.

This press release includes forward-looking statements. For these statements, ImmunoGen claims the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. It should be noted that there are risks and uncertainties related to the development of novel anticancer products, including mirvetuximab soravtansine (IMGN853), including risks related to clinical studies and regulatory processes, their timings and results. A review of these risks can be found in ImmunoGen's Annual Report on Form 10-K for the fiscal year ended June 30, 2015 and other reports filed with the Securities and Exchange Commission.