Antisoma presents positive PSA data from AS1404 phase II trial in prostate cancer

    London, UK and Boston, Mass: 18 September 2006 - Cancer drug
developer Antisoma plc (LSE: ASM, US OTC: ATSMY) announces the
presentation of the first findings from its ongoing phase II trial of
AS1404 in hormone-refractory prostate cancer. These show a markedly
higher rate of PSA responses among men receiving AS1404. Preliminary
data from the first 64 of 74 patients in the trial show a PSA
response rate of 57% in those receiving AS1404 plus docetaxel
chemotherapy compared with 35% in those receiving docetaxel alone. In
addition, the proportion of men showing disease progression by PSA
was almost halved in the AS1404 group (17% versus 29% with docetaxel
alone).  The findings were presented yesterday at the Tumor
Microenvironment meeting in Boston by Dr Gary Acton, Antisoma's Chief
Medical Officer.

PSA is a protein, prostate-specific antigen. Levels of PSA in the
blood are used in the diagnosis of prostate cancer and the tracking
of responses to its treatment. PSA is one of the most widely
recognised disease markers in oncology, and PSA responses have been
related to clinical outcomes in numerous studies.

As well as the PSA data, Dr Acton reviewed safety findings to date
from the trial. These show that addition of AS1404 to docetaxel
chemotherapy has been generally well-tolerated, without exacerbation
of chemotherapy side-effects.

Commenting, Glyn Edwards, CEO of Antisoma, said: "These positive data
from our phase II prostate cancer trial of AS1404 are a further
important demonstration of the drug's effects. They complement the
positive survival, progression and response data already presented
from our lung cancer trial, and show that the potential of AS1404
extends to two of the big four cancer indications. The findings
underline again our leading position in the development of vascular
disrupting agents and reinforce our confidence that we are well
placed to strike a partnering deal for AS1404."

Enquiries:


Glyn Edwards, Chief Executive Officer
Daniel Elger, Director of Communications                     +44
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                                                             8200
Antisoma
plc

Mark Court/Lisa Baderoon/Rebecca Skye Dietrich
Buchanan Communications                                      +44
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Antisoma disclaimer
Certain matters discussed in this statement are forward looking
statements that are subject to a number of risks and uncertainties
that could cause actual results to differ materially from results,
performance or achievements expressed or implied by such statements.
These risks and uncertainties may be associated with product
discovery and development, including statements regarding the
company's clinical development programmes, the expected timing of
clinical trials and regulatory filings. Such statements are based on
management's current expectations, but actual results may differ
materially.

Details of the PSA findings
Data are currently available from 64 of the 74 men participating in
the trial. PSA response is defined as a 50% or greater reduction in
PSA level from baseline, in accordance with the Bubley criteria
(Eligibility and response guidelines for phase II clinical trials in
androgen-independent prostate cancer: recommendations from the
Prostate-Specific Antigen Working Group. Journal of Clinical Oncology
1999, Volume 17, pp 3461-67). On this measure, of the 64 men
currently evaluable, 17/30 in the AS1404 + docetaxel group and 12/34
in the docetaxel alone group, had PSA responses. Of these, all but
three in each group have already been confirmed by a second reading 6
weeks after the initial result. The other three responses in each
group are unconfirmed pending data from further tests. Progression by
PSA is defined as a 25% or greater increase. Among the first 64
patients, five in the AS1404 + docetaxel group and ten in the
docetaxel alone group showed progressive disease by this measure.

Background on AS1404
AS1404 (DMXAA) is a small-molecule vascular disrupting agent which
targets the blood vessels that nourish tumours. The drug was
discovered by Professors Bruce Baguley and William Denny and their
teams at the Auckland Cancer Society Research Centre, University of
Auckland, New Zealand. It was in-licensed by Antisoma from Cancer
Research Ventures Limited (now Cancer Research Technology) in August
2001.

Background on Antisoma
Based in London, UK, Antisoma is a biopharmaceutical company that
develops novel products for the treatment of cancer. Antisoma fills
its development pipeline by acquiring promising new product
candidates from internationally recognised academic or cancer
research institutions. Its core activity is the preclinical and
clinical development of these drug candidates. Please visit
www.antisoma.com for further information.

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