ImmunoGen Announces Mature Data from FORWARD II Expansion Cohort Evaluating Mirvetuximab Soravtansine in Combination with Avastin® in Ovarian Cancer

Results to be Presented at 2019 ASCO Annual Meeting

Combination Demonstrates Significant Anti-Tumor Activity and
Favorable Safety and Tolerability in Platinum-Resistant Disease

Findings Support Ongoing Studies of Doublet Combination in
Platinum-Agnostic Disease and Triplet in Platinum-Sensitive Patients

WALTHAM, Mass.–(BUSINESS WIRE)–ImmunoGen,
Inc.
, (Nasdaq: IMGN), a leader in the expanding field of
antibody-drug conjugates (ADCs) for the treatment of cancer, today
announced mature data from the FORWARD II expansion cohort evaluating
mirvetuximab soravtansine in combination with Avastin®
(bevacizumab) in patients with folate receptor alpha (FRα)-positive
platinum-resistant ovarian cancer. These findings will be presented at
the 2019 American Society of Clinical Oncology (ASCO) Annual Meeting,
which is being held May 31 – June 4 in Chicago, IL.

“We are pleased that the combination of mirvetuximab plus Avastin has
generated significant anti-tumor activity in patients with
platinum-resistant disease, with trends toward deeper, more durable
responses seen in individuals with higher FRα expression and a favorable
tolerability profile. The outcomes observed in patients with medium or
high FRα expression are encouraging with respect to those reported in
similar patient populations for Avastin plus chemotherapy,” said Anna
Berkenblit, M.D., Vice President and Chief Medical Officer of ImmunoGen.
“Our goal remains to establish mirvetuximab as the combination agent of
choice in ovarian cancer, supporting its use in earlier lines of
therapy. These mature data support further exploration of this doublet,
as well as the ongoing expansion study evaluating a triplet combination
of mirvetuximab with Avastin and carboplatin in patients with
platinum-sensitive disease.”

DATA FROM FORWARD II EXPANSION COHORT WITH AVASTIN

Mirvetuximab soravtansine in combination with Avastin in patients with
FRα-positive platinum-resistant ovarian cancer continues to demonstrate
anti-tumor activity with durable responses and a favorable tolerability
profile, particularly among the subset of patients who have received up
to two prior lines of therapy and have medium or high levels of FRα
expression.

Key findings in 66 patients with platinum-resistant disease include:

  • In the subset of 16 Avastin-naïve patients with medium or high FRα
    expression who have received up to two prior lines of therapy, the
    confirmed overall response rate (ORR) was 56 percent (95% CI 30,80),
    with a median progression-free survival (PFS) of 9.9 months (95% CI
    4.1,15.9) and a median duration of response (DOR) of 12 months (95% CI
    6,14.9).
  • In the overall patient population, the confirmed ORR was 39 percent
    (95% CI 28,52), with a median PFS of 6.9 months (95% CI 4.9,8.6) and a
    median DOR of 8.6 months (95% CI 4.9, 14.9).
  • The combination continues to display a safety profile in-line with the
    known profiles of each agent, with no new safety signals identified.

“Current treatment options for patients with platinum-resistant ovarian
cancer have, unfortunately, exhibited limited efficacy with challenging
side effects,” stated David O’Malley, M.D., Professor, Director of
Gynecology Clinical Trials and Phase 1 Program, James Cancer Center and
The Ohio State University Wexner Medical Center, and FORWARD II
Principal Investigator. “Final results from the combination of
mirvetuximab soravtansine and Avastin expansion cohort demonstrate very
encouraging activity and good tolerability in platinum-resistant ovarian
cancer patients, especially those with medium or high FRα expression
levels. I look forward to further evaluating mirvetuximab in combination
with Avastin as well as in the triplet with carboplatin.”

ASCO PRESENTATION DETAILS

  • Title: “Mirvetuximab soravtansine, a folate receptor alpha
    (FRα)-targeting antibody-drug conjugate (ADC), in combination with
    bevacizumab in patients (pts) with platinum-resistant ovarian cancer:
    Final findings from the FORWARD II study”
  • Day/Time: Saturday, June 1, 1:15pm – 4:15pm CDT and discussed
    at the Poster Discussion Session, 4:30pm-6pm CDT in S406
  • Lead Author: David M. O’Malley, M.D., The Ohio State University
    College of Medicine
  • Location: Hall A
  • Abstract: 5520

Initial data from an investigator-sponsored trial through the National
Comprehensive Cancer Network evaluating mirvetuximab in combination with
gemcitabine in patients with FRα-positive recurrent epithelial ovarian,
endometrial, or triple negative breast cancer will also be presented.
Full dose mirvetuximab appears to combine well with gemcitabine, with a
safety profile as expected for these agents and with encouraging
anti-tumor activity seen in all three tumor types.

  • Title: “A phase 1 study of mirvetuximab soravtansine (IMGN853)
    and gemcitabine (G) in patients with FOLR1-positive recurrent
    epithelial ovarian (EOC), endometrial cancer (EC), or triple-negative
    breast cancer (TNBC)”
  • Day/Time: Saturday, June 1, 8:00am – 11:00am CDT and discussed
    at the Poster Discussion Session, 3:00pm-4:30pm CDT in E450
  • Lead Author: Mihaela C. Cristea, MD, City of Hope
  • Location: Hall A
  • Abstract: 3009

Additional information can be found at www.asco.org.

ABOUT FORWARD II

FORWARD II is a Phase 1b/2 study of mirvetuximab in combination with
Avastin (bevacizumab), carboplatin or Keytruda (pembrolizumab) in
patients with FRα-positive platinum-resistant or platinum-agnostic
ovarian cancer, primary peritoneal, or fallopian tube tumors, as well as
a triplet combination of mirvetuximab plus carboplatin and Avastin in
patients with platinum-sensitive ovarian cancer.

ABOUT MIRVETUXIMAB SORAVTANSINE

Mirvetuximab soravtansine (IMGN853) is the first folate receptor alpha
(FRα)-targeting ADC. It uses a humanized FRα-binding antibody to target
the ADC specifically to FRα-expressing cancer cells and a potent
anti-tumor agent, DM4, to kill the targeted cancer cells.

ABOUT IMMUNOGEN

ImmunoGen is developing the next generation of antibody-drug conjugates
(ADCs) to improve outcomes for cancer patients. By generating targeted
therapies with enhanced anti-tumor activity and favorable tolerability
profiles, we aim to disrupt the progression of cancer and offer our
patients more good days. We call this our commitment to “target a better
now.” The Company has built a productive platform generating a broad
pipeline of ADCs targeting solid tumors and hematologic malignancies.

Learn more about who we are, what we do, and how we do it at www.immunogen.com.

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

FORWARD-LOOKING STATEMENTS

This press release includes forward-looking statements based on
management’s current expectations. These statements include, but are not
limited to, ImmunoGen’s expectations related to: the occurrence, timing
and outcome of potential pre-clinical, clinical and regulatory events
related to the Company’s and its collaboration partners’ product
programs; and the presentation of preclinical and clinical data on the
Company’s and collaboration partners’ product candidates. 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. Various factors could cause ImmunoGen’s actual
results to differ materially from those discussed or implied in the
forward-looking statements, and you are cautioned not to place undue
reliance on these forward-looking statements, which are current only as
of the date of this release. Factors that could cause future results to
differ materially from such expectations include, but are not limited
to: the timing and outcome of ImmunoGen’s and the Company’s
collaboration partners’ research and clinical development processes; the
difficulties inherent in the development of novel pharmaceuticals,
including uncertainties as to the timing, expense and results of
preclinical studies, clinical trials and regulatory processes;
ImmunoGen’s ability to financially support its product programs;
ImmunoGen’s dependence on collaborative partners; industry merger and
acquisition activity; and other factors more fully described in
ImmunoGen’s Annual Report on Form 10-K for the year ended December 31,
2018 and other reports filed with the Securities and Exchange Commission.

Contacts

INVESTOR RELATIONS CONTACT
Sarah Kiely
781-895-0600
sarah.kiely@immunogen.com

MEDIA CONTACT
Courtney O’Konek
781-895-0600
courtney.okonek@immunogen.com

OR

FTI Consulting
Robert Stanislaro
212-850-5657
robert.stanislaro@fticonsulting.com