Contacts:

Barbara Sullivan Sullivan& Associates (714) 374-6174 bsullivan@sullivanpr.com

Christina Andrian diaDexus, Inc. (650) 246-6476 candrian@diadexus.com

DIADEXUS LAUNCHES COLLABORATION TO EVALUATE THE ROLE OF BREAST TUMOR GENES IN THE TREATMENT OF BREAST CANCER

South San Francisco, CA - January 10, 2007 - diaDexus, Inc., a privately held biotechnology company, announced a collaboration with Mayo Validation Support Services to investigate a test featuring a select panel of tumor-specific genes to aid in patient risk stratification and assist in chemotherapy treatment decisions for breast cancer patients. The test uses gene expression profiling to predict recurrence of malignancy in patients diagnosed with primary invasive early stage breast cancer.

Previous study data presented by diaDexus at the 2005 San Antonio Breast Cancer Symposium demonstrated that a set of eight genes were differentially expressed in patients who presented with progressive disease, compared with those who were disease-free after a median follow-up of 70 months, suggesting that the PCR-based test involving these genes warrants additional investigation into its utility in identifying patients at higher risk for recurrence.

The Mayo collaboration is part of diaDexus’ molecular diagnostics program focused on developing tests to aid in the prognosis and staging of breast, colorectal, and prostate cancers. PCR (polymerase chain reaction) is a technique for amplifying DNA or RNA sequences in a laboratory in order to facilitate diagnostic testing or research.

In this larger confirmatory study with Mayo Validation Support Services, diaDexus investigators will evaluate whether the test, which includes the previously identified eight genes in addition to others, can help provide breast cancer patients with personalized prognostic information. This critical information may help physicians determine the need for chemotherapy and help improve cancer management.

The study will include tumor samples from 60 breast cancer patients who have been tracked for up to 10 years following diagnosis and initial treatment. Comparisons will be made between “good outcome” patients who showed no disease progression during 5–10 years of follow-up (30 cases), and “poor outcome” patients whose disease progressed within five years of surgery (30 cases). A control group will consist of six normal breast tissue samples.

According to Roberto Macina, diaDexus’ director of molecular technology, the study is a significant step in testing the value of diaDexus’ extensive cancer diagnostic portfolio for the management of breast cancer. “Our goal is to provide physicians and cancer patients with clinically valuable information that will help identify those patients with a poor prognosis who would benefit from chemotherapy, while helping to avoid chemotherapy—and its often-debilitating side effects—in those predicted to have good outcomes,” Macina said.

About Mayo Validation Support Services
Mayo Validation Support Services, an affiliate of Mayo Clinic, based in Rochester, Minn., assists pharmaceutical, biotechnology, and diagnostic companies in the preclinical validation of promising targets, lead compounds, biomarkers, and tests. Mayo’s contribution of well-annotated biospecimens and clinical follow-up data support the development of individualized medicine, one of Mayo’s strategic initiatives.

About diaDexus
diaDexus, Inc., based in South San Francisco, is focused on the discovery, development, and commercialization of clinically valuable, patent-protected diagnostic products. In addition to its cancer diagnostics program, the company’s first commercial product focuses on heart disease and stroke risk. The PLAC® test is a simple blood test that measures levels of a new risk factor for coronary heart disease and stroke—lipoprotein-associated phospholipase A2 (Lp-PLA2), a cardiovascular-specific inflammatory marker implicated in the formation of vulnerable, rupture-prone plaque. For more information, visit www.plactest.com or www.diaDexus.com.