Clinical Data Presented at ESMO Shows ETAG(TM) System's Potential in Predicting Response to Cancer Treatment

Clinical Data Presented at ESMO Shows ETAG(TM) System's Potential
in Predicting Response to Cancer Treatment 


MOUNTAIN VIEW, Calif., Nov. 4  /PRNewswire-FirstCall/ -- ACLARA BioSciences
(NASDAQ:ACLA) today announced that Sharat Singh, Ph.D., ACLARA's Chief
Technical Officer, presented data from a pilot clinical trial demonstrating the
ability of ACLARA's eTag(TM) assays to correctly differentiate responders from
non-responders to Herceptin(R) treatment in patients with breast cancer. These
data, subject to confirmation in larger, trials, suggest that the eTag System
may be more accurate than the current standard at differentiating responders
from non-responders to this widely used targeted therapy.  Dr. Singh's oral
presentation was made at the "Advances in Her2 Profiling" session of the 29th
European Society for Medical Oncology (ESMO) Congress held this week in Vienna.

"The scientific and clinical oncology community is eager to have biomarkers
that accurately predict an individual patient's response to a particular
targeted cancer treatment, and the results of this feasibility experiment were
well-received at ESMO," said Dr. Singh.  "The critical information these
biomarkers can potentially offer will contribute to the development of truly
personalized medicine.  The results of this initial experiment, while involving
a limited number of patient samples, demonstrate the potential of eTag(TM)
assays to provide this type of vital prognostic information."

Dr. Singh's presentation, "The use of ErbB activation status as prognostic
markers in breast cancer patients treated with Herceptin(R)", described a set
of feasibility experiments which were conducted on blinded sets of
formalin-fixed, paraffin-embedded tissue samples from 13 breast cancer patients
treated with Herceptin(R) and chemotherapy.  All patients were positive for the
Her2 receptor, the molecular target of Herceptin(R), as measured by
HercepTest(R), one of the standard commercial assays for Herceptin(R)
pre-screening, and were consequently treated with Herceptin(R). Nonetheless, 5
of the 13 patients had objective tumor responses, 4 had stable disease, and the
remaining 4 had progressive disease.

By contrast, the eTag assays, which were designed to measure receptor dimer
levels as an indicator of pathway activation as opposed to simple receptor
expression, were able to more fully differentiate responders from
non-responders.  Specifically, medium to high levels of Her2 homodimers as
measured by eTag assays had a positive correlation with response, but when
coupled with high levels of Her3 heterodimers as measured by eTag assays (a
potential biomarker for an alternative growth pathway not blocked by
Herceptin(R)) had a negative correlation with response.  All 5 patients with
objective tumor response had high levels of Her2 homodimers and low levels of
Her3 heterodimers.  All 4 patients with stable disease had low to medium levels
of Her3 heterodimers, while all 4 patients with progressive disease had high
levels of Her3 heterodimers.

Larger studies are needed to provide additional validation for this approach,
and these encouraging results have led ACLARA and the Tokyo Metropolitan
Institute of Medical Science (Rinshoken) to collaborate on a larger,
confirmatory study, the planning of which is currently underway.

About ACLARA

Founded in 1995, ACLARA is a biotechnology company working to provide
physicians and researchers products and services to make personalized medicine
a reality through its protein-based assay technology -- the eTag(TM) System.
ACLARA is dedicated to unlocking the power of pathway biology to accelerate the
development of next-generation targeted therapeutics, recognizing the most
appropriate patients for approved therapies and identifying the
highly-specific, protein-based biomarkers that will enable physicians to create
truly personalized treatment regimens for patients suffering from cancer and
other life-threatening disorders.

ACLARA is commercializing its proprietary eTag System to enhance and accelerate
drug discovery research and the preclinical and clinical development of
targeted therapeutics. ACLARA's technology may also enable the development of
highly specific, protein-based diagnostics capable of providing physicians with
a powerful tool for creating personalized treatment regimens for patients
suffering from serious and difficult-to-treat cancers.  For more information on
ACLARA please visit the Company's web site at http://www.aclara.com/.

Forward-Looking Statements

All statements in this news release that are not historical are forward-looking
statements within the meaning of the Securities Exchange Act of 1934 as
amended. Such forward-looking statements are subject to factors that could
cause actual results to differ materially for ACLARA from those projected. 
Those factors include risks and uncertainties relating to the performance of
our products, anticipated progress in commercialization of our eTag(TM) Assay
System; the potential for use of our eTag assays in clinical development
programs; the potential for use of our eTag assays as diagnostic tests; our
ability to successfully conduct clinical studies and the results obtained from
those studies; whether the results from larger studies will confirm initial
results from smaller pilot or feasibility studies, our ability to establish
reliable, high-volume operations at commercially reasonable costs; expected
reliance on a few customers for the majority of our revenues; actual market
acceptance of our products and adoption of our technological approach and
products by pharmaceutical and biotechnology companies; our estimate of the
size of our markets; our estimates of the levels of demand for our products;
our ability to develop organizational capabilities suitable for the further
development and commercialization of our eTag assays; the ultimate validity and
enforceability of our patent applications and patents; the possible
infringement of the intellectual property of others; technological approaches
of ACLARA and our competitors; our pending merger with ViroLogic, Inc.,
including the risk that the closing conditions or the merger may not be
satisfied and the merger may not be completed, and costs related to the
proposed merger; and other risk factors identified in our Form 10-Q for the
quarter ended June 30, 2004 and in the Joint Proxy/Prospectus related to our
proposed merger with ViroLogic, Inc. as filed with the Securities and Exchange
Commission.

Trademarks

ACLARA BioSciences is a registered trademark, and eTag and the ACLARA logo are
trademarks of ACLARA BioSciences, Inc.  Herceptin and HercepTest are registered
trademarks of Genentech, Inc. and DakoCytomation, respectively. 

DATASOURCE: ACLARA BioSciences Inc.



CONTACT:  Alfred Merriweather, VP, Finance and CFO of ACLARA Biosciences,

[phone], or 



Web site:  http://www.aclara.com/

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