Phase III Study Results Showed Eisai's Eribulin Mesylate Significantly Improved Overall Survival in Patients With Locally Recurrent or Metastatic Breast Cancer

Global EMBRACE Study Compared Eribulin to Treatment of Physician's Choice

CHICAGO, June 6, 2010 - Results of a Phase III study presented today at the American
Society of Clinical Oncology (ASCO) Annual Meeting showed that Eisai's
eribulin mesylate significantly improved median overall survival (OS)
compared with Treatment of Physician's Choice (TPC) in heavily pre-treated
metastatic breast cancer patients.[1]

These results were presented as part of an ASCO-sponsored press
briefing; additional details from the study will be presented in an oral
session on June 8, 2010 at 9:30 a.m. in East Hall D1 at Chicago's McCormick
Place. The study abstract has also been selected for presentation at the 2010
Best of ASCO(R) Meetings, which will be held in San Francisco and Boston in
the United States and in several countries around the world in the months
following the ASCO Annual Meeting.

The Phase III "EMBRACE" study (Eisai Metastatic Breast Cancer
Study Assessing Physician's Choice Versus Eribulin E7389) met its primary
endpoint of overall survival, showing that patients who received eribulin
survived a median of 2.5 months longer than patients who received TPC
(overall survival of 13.12 months versus 10.65 months, respectively,
p=0.04).[1] Results from EMBRACE also showed that a secondary endpoint of
overall response rate (ORR) was statistically significant. Another secondary
endpoint, progression free survival (PFS), was supportive of the primary
endpoint but did not reach statistical significance.[2]

"To date, no single-agent Phase III clinical trial has
demonstrated improved survival in women with heavily pre-treated metastatic
breast cancer," said Chris Twelves, M.D., lead investigator for the EMBRACE
study and Professor of Clinical Cancer Pharmacology and Oncology from the
University of Leeds and St. James's University Hospital, Leeds, United
Kingdom. "These results showed that eribulin significantly improved overall
survival versus a variety of agents used in a real-world setting, which
previously no single agent has shown."

The most frequently reported adverse events (AEs) among patients
treated with eribulin were asthenia, or fatigue (53.7%), neutropenia, or low
white blood cell counts (51.7%), alopecia, or hair loss (44.5%) and
peripheral neuropathy, or numbness and tingling in different parts of the
body (34.6%). Treatment-emergent serious AEs were reported for 25 percent of
patients in the eribulin group and 25.9 percent of patients in the TPC
arm.[2]

About the Study

EMBRACE was an open-label, randomized, multi-center study of 762
patients with locally recurrent or metastatic breast cancer who were
previously treated with at least two and a maximum of five prior
chemotherapies ([greater than or equal to]2 for advanced disease), including
an anthracycline and a taxane. Patients must have been refractory to the most
recent chemotherapy, documented by progression on or within six months of
therapy.[1] The study was designed to compare overall survival in patients
treated with eribulin versus a TPC arm, reflecting a real-world clinical
setting where a variety of agents are used to treat patients with advanced
breast cancer. [1]

Patients were randomized in a two-to-one ratio to receive either
eribulin (1.4 mg/m[2] administered intravenously for two-to-five minutes on
days 1 and 8 of a 21-day treatment cycle) or TPC.[1] TPC was defined as any
single agent chemotherapy, hormonal treatment or biological therapy approved
for the treatment of cancer; or palliative radiotherapy administered
according to local practice.[2] The median age of study participants was 55
(range 27-85); 16 percent of patients had HER2 positive breast cancer and 19
percent had breast cancer that was negative for estrogen, progesterone and
HER2 receptors (triple-negative breast cancer).[1]

About Metastatic Breast Cancer

Worldwide, more than one million women a year are diagnosed with
breast cancer.[3] Approximately 50 percent of women worldwide initially
diagnosed with breast cancer are expected to develop recurrent or metastatic
disease within 15 years of their first diagnosis.[4,5] Only one in five women
with metastatic breast cancer survives longer than five years.[6] In the
United States, an estimated 155,000 women are currently living with
metastatic breast cancer, and that number is projected to increase to 162,000
by 2011.[7]

"Women with advanced breast cancer are in critical need of new
treatment options," said Alton Kremer, M.D., Ph.D, Global Head of Clinical
Development for Oncology at Eisai Inc. "In this study, eribulin has shown an
improvement in survival, and if approved by health authorities, it may offer
patients a new treatment option at this stage of the disease."

About Eribulin

Eribulin mesylate (E7389) is an investigational agent being evaluated as
a potential treatment for locally advanced or metastatic breast cancer. A
non-taxane, microtubule dynamics inhibitor, eribulin is a synthetic analog of
halichondrin B, which is derived from a natural product isolated from the
marine sponge Halichondria okadai.

On March 30, 2010, Eisai announced it had submitted simultaneous
regulatory applications for approval of eribulin mesylate for the treatment
of locally advanced or metastatic breast cancer to agencies in Japan, the
United States and the European Union (EU). The eribulin New Drug Application
(NDA) was granted priority review status by the U.S. Food and Drug
Administration (FDA) on May 28, 2010.

Eisai Oncology

Eisai Oncology is dedicated to discovering, developing and producing
innovative oncology therapies that can make a difference and impact the lives
of patients and their families. This passion for people is part of Eisai's
human health care (hhc) mission, which strives for better understanding of
the needs of patients and their families to increase the benefits health care
provides. Our commitment to meaningful progress in oncology research, built
on scientific expertise, is supported by a global capability to conduct
discovery and preclinical research, and develop small molecules, therapeutic
vaccines, biologic and supportive care agents for cancer across multiple
indications.

Eisai Inc.

Eisai Inc. was established in 1995 and is ranked among the top-20
U.S. pharmaceutical companies (based on retail sales). The company began
marketing its first product in the United States in 1997 and has rapidly
grown to become a fully integrated pharmaceutical business with fiscal year
2009 (year ended March 31, 2010) sales of approximately $3.9 billion. Eisai's
areas of commercial focus include neurology, gastrointestinal disorders and
oncology/critical care. The company serves as the U.S. pharmaceutical
operation of Eisai Co., Ltd.

Eisai has a global product creation organization that includes
U.S.-based R&D facilities in Maryland, Massachusetts, New Jersey, North
Carolina and Pennsylvania as well as manufacturing facilities in Maryland and
North Carolina. The company's areas of R&D focus include neuroscience;
oncology; vascular, inflammatory and immunological reaction; and
antibody-based programs. For more information about Eisai, please visit
www.eisai.com.

Eisai Europe, Ltd.

Eisai concentrates its R&D activities in three key areas:

    - Integrative Neuroscience, including: Alzheimer's disease, multiple
      sclerosis, neuropathic pain, epilepsy, depression

    - Integrative Oncology, including: anticancer therapies; tumor
      regression, tumor suppression, antibodies and supportive cancer
      therapies; pain relief, nausea

    - Vascular/Immunological reaction, including: acute coronary syndrome,
      atherothrombotic disease, severe sepsis, rheumatoid arthritis,
      psoriasis, Crohn's disease

In Europe, Eisai undertakes sales and marketing operations in
over 20 markets, including the United Kingdom, France, Germany, Italy, Spain,
Switzerland, Sweden, Ireland, Austria, Denmark, Finland, Norway, Portugal,
Iceland, Czech Republic, Hungary and Slovakia.

Eisai Co., Ltd.

Eisai Co., Ltd. is a research-based human health care (hhc)
company that discovers, develops and markets products throughout the world.
Through a global network of research facilities, manufacturing sites and
marketing subsidiaries, Eisai actively participates in all aspects of the
worldwide health care system. Eisai employs approximately 11,000 employees
worldwide.

For further information, please visit www.eisai.co.jp.

* Best of ASCO(R) is a registered trademark of the American
Society of Clinical Oncology

References

[1] Twelves C et al. A Phase III Study (EMBRACE) of Eribulin Mesylate vs
Treatment of Physician's Choice in Patients with Locally Recurrent or
Metastatic Breast Cancer Previously Treated with an Anthracycline and a
Taxane. Abstract 1084, American Society of Clinical Oncology (ASCO) congress,
Chicago, 2010.

[2] Eisai - Data on file.

[3] Coughlin, S. Breast cancer as a global health concern. Cancer
Epidemiology, October 2009; 33: 315-18.

[4] Cardoso F and Castiglione M. Locally recurrent or metastatic breast
cancer: ESMO Clinical Recommendations for diagnosis, treatment and follow-up.
Annals of Oncology, 2009; 20(4): iv15-iv18.

[5] Jatoi I et al. Hazard rates of recurrence following diagnosis of
primary breast cancer. Breast Cancer Research and Treatment, 2005; 89:
173-78.

[6] Gonzalez-Angulo AM et al. Overview of Resistance to Systemic Therapy
in Patients with Breast Cancer. Breast Cancer Chemosensitivity (Advances in
Experimental Medicine and Biology, Vol. 608), 2007; 1-16.

[7] AdvancedBC.org. Overcoming Isolation and Exposing
Misconceptions. Bridging Gaps & Expanding Outreach for Metastatic Breast
Cancer, September 2008. Available at www.advancedbc.org/node/25 (last
accessed 05/28/10).

Media Inquiries: Judee Shuler, Eisai Inc., During ASCO: +1-908-337-2540, +1-201-746-2241 (office). Cressida Robson, Eisai Europe Ltd., During ASCO: +44-7908-314-155. Investor Inquiries: Dave Melin, Eisai Inc., +1-908-255-6378 (cell).