Quest Diagnostics Incorporated , the nation's leading provider of diagnostic testing, information and services, announced today that it has entered into a non- exclusive license agreement for the heteroduplex tracking technology underlying Pathway Diagnostics' SensiTrop™ HIV co-receptor tropism test. Tropism refers to the way a virus targets host cells. A molecular-based assay for HIV co-receptor tropism will help physicians personalize therapy for HIV patients. Quest Diagnostics is the first full-service national clinical laboratory in the U.S. to license the technology. Terms of the agreement were not disclosed.

"Pathway Diagnostics' heteroduplex tracking technology is an important new advance that highlights the growing importance of diagnostics to personalized medicine," said Joyce G. Schwartz, M.D., vice president and chief laboratory officer. "HIV co-receptor tropism tests can help physicians identify which patients, of the estimated 500,000 people in the U.S. being treated for HIV infection, will benefit from entry inhibitor drugs, the latest development in life-enhancing anti-retroviral therapies."

Pathway Diagnostics' SensiTrop technology is designed to enable physicians to identify the HIV co-receptor tropism status of a patient infected with HIV, the virus that causes AIDS. HIV co-receptor tropism refers to the preference of strains of HIV to bind, activate and infect cells, promoting disease progression, according to the type of co-receptor, specifically CXCR4 (X4) and CCR5 (R5), on the surface of the cell. Entry inhibitor anti-retroviral drugs, such as Pfizer's Selzentry™ therapy, which is the first in its class to be FDA approved, block the CCR5 co-receptor to inhibit disease progression.

Selzentry clinical trials showed that patients infected with CXCR4 or X4/R5 viral mixtures were at an increased risk for treatment failure taking Selzentry, and therefore should not receive the drug. Pathway Diagnostics' technology detects the CXCR4 HIV co-receptor in patient samples that have as little as one percent CXCR4-tropic virus, enabling physicians to identify with a high degree of accuracy those patients with X4-tropic virus who are unlikely to benefit from, and should not receive, treatment with entry inhibitor therapies. The heteroduplex tracking technology, which is molecular based, also can yield test results within seven days of receiving a specimen, compared to up to four weeks to receive results with cellular-based methods. During the first quarter 2008, Quest Diagnostics expects to develop an in- house laboratory validated assay based on the licensed technology. Until then and beginning November 1, 2007, physicians may order SensiTrop through Quest Diagnostics, which will refer the test to Pathway Diagnostics.

"Offering a molecular-based HIV co-receptor tropism assay through Quest Diagnostics will give the greatest number of patients the opportunity to take advantage of Selzentry and future drug therapies in its class," said Walter Narajowski, chief executive officer, Pathway Diagnostics. "Quest Diagnostics' top-tier scientific and medical staff track record of quality, innovation, and service excellence distinguishes it as a front runner in the race to provide diagnostics that will help physicians potentially delay disease progression and the onset of AIDS in their HIV-infected patients."

About HIV and AIDS

HIV, or the human immunodeficiency virus, is a retrovirus that infects cells of the human immune system, destroying or impairing their function. The most advanced stage of HIV infection is AIDS, or acquired immunodeficiency syndrome. HIV can take up to 15 years to develop into AIDS, a process that antiretroviral drugs can help delay. The World Health Organization estimates that approximately 1.2 million people over the age of 15 in the U.S. were infected with HIV in 2005, the most recent year for which data is available.

About Pathway Diagnostics

Pathway Diagnostics Corporation focuses on the development, validation and performance of novel, proprietary biomarker assays across multiple disease areas that address unmet medical needs and improve patient care. The company combines assay development expertise with a broad range of advanced technology platforms, a fully licensed CLIA laboratory, and a growing portfolio of patent-protected biomarkers for pharmaceutical companies to use in drug development and for commercial reference laboratories and in vitro diagnostic manufacturers to license for use in patient testing. Pathway effectively bridges the gap between biomarker research and biomarker testing, as well as ensures a regulatory-compliant environment for laboratory testing for preclinical and clinical drug development programs. Additional company information is available at www.pathwaydx.com.

About Quest Diagnostics

Quest Diagnostics is the leading provider of diagnostic testing, information and services that patients and doctors need to make better healthcare decisions. The company offers the broadest access to diagnostic testing services through its national network of laboratories and patient service centers, and provides interpretive consultation through its extensive medical and scientific staff. Quest Diagnostics is a pioneer in developing innovative new diagnostic tests and advanced healthcare information technology solutions that help improve patient care. Additional company information is available at www.questdiagnostics.com.

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This communication contains certain forward-looking statements. These forward-looking statements, which may include, but are not limited to, statements concerning the proposed acquisition, are based on management's current expectations and estimates and involve risks and uncertainties that could cause actual results or outcomes to differ materially from those contemplated by the forward-looking statements. Certain of these risks and uncertainties may include, but are not limited to the risks and uncertainties described in the Quest Diagnostics Incorporated 2006 Form 10-K and subsequent filings.

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SOURCE: Quest Diagnostics Incorporated

CONTACT: Investors: Laure Park, +1-973-520-2900, or Media: Nancy
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Web site: http://www.questdiagnostics.com/
http://www.pathwaydx.com/