Trubion Announces Positive Data From a Phase 1 / 2 Study of TRU-016 for the Treatment of Chronic Lymphocytic Leukemia (CLL)

SEATTLE and ORLANDO, Fla. — Trubion Pharmaceuticals, Inc. (Nasdaq: TRBN) announced today the presentation of encouraging Phase 1 safety and efficacy results following administration of low doses of TRU-016 in heavily pre-treated patients with high-risk genomic factors and relapsed or refractory chronic lymphocytic leukemia (CLL).

TRU-016 is the Company’s proprietary anti-CD37 Small Modular ImmunoPharmaceutical (SMIP(TM)) product candidate.

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Abstract 3017: A Phase 1 Trial of TRU-016, An Anti-CD37 Small Modular ImmunoPharmaceutical (SMIP(TM)), in Relapsed and Refractory CLL — Early Promising Clinical Activity

The clinical data presented at the American Society of Clinical Oncology (ASCO) are preliminary results from an ongoing Phase 1 / 2 clinical trial (#16007) of TRU-016 for the treatment of CLL and small lymphocytic leukemia (SLL). The objectives of the Phase 1 TRU-016 CLL study were to define safety and tolerability, identify a maximum tolerated dose, evaluate pharmacology and pharmacodynamics, and assess preliminary clinical activity. Patients received either one dose weekly for four weeks, or three doses the first week followed by three additional weekly doses. Patients were also able to receive up to two additional cycles if clinical benefit was observed.

At the time of the presentation, data were available for 26 patients enrolled in the Phase 1 dose escalation trial, all of whom had received an average of 6.5 prior treatments, including at least one fludarabine-containing regimen. All patients had also previously received rituximab or other anti-CD20 therapies an average of three times, either as a single agent or as part of a combination regimen. Of the 24 patients with genetic data, 17 had high genomic risk factors, such as deletion of the 17p or 11q chromosomes. At the time of the presentation, patients had received intravenous doses of TRU-016 ranging from 0.03 mg/kg to 10 mg/kg over the course of four to 12 weeks.

Beginning with the 0.1 mg/kg dose, evidence of biologic activity was observed. The median reduction in peripheral lymphocytes was 67% and was as high as 98%. Two patients with leukemia cutis had complete or partial clearance of skin lesions. One patient had a 36% reduction in lymph node size, a 28% decrease in spleen size and a significant increase (44%) in hemoglobin. Mild grade 1 or 2 infusion toxicity was observed and there were three dose-limiting toxicities reported that all occurred in different dose cohorts. A maximum tolerated dose has not yet been reached.

Also presented at the ASCO Annual Meeting this week was data demonstrating that TRU-016 is additive or synergistic in combination with established therapeutics (Abstract 8571) and that TRU-016-mediated apoptosis in CLL cells occurs via a distinct mechanism of apoptosis compared with many other therapeutic agents utilized for the treatment of CLL (Abstract 3035). Copies of all three presentations are available on Trubion’s website at http://investors.trubion.com/events.cfm.

“These results show promising single agent activity of TRU-016, even at surprisingly low doses, in a heavily pre-treated patient population most of whom harbored genetic lesions known to be associated with poor response to standard therapies,” said Peter Thompson, M.D., FACP, president, CEO and chairman of Trubion. “These data suggest that this novel, first-in-class compound may become a new treatment option for patients with B-cell malignancies, either as a stand-alone treatment or when used in combination with other therapies. These diseases are not curable presently, and eventually patients with these diseases show diminished response to current therapies. These patients and their physicians need more effective therapies with new mechanisms of action that address new targets. We look forward to presenting additional data on our expanding clinical experience with TRU-016 as it is accrued.”

TRU-016 is a humanized, SMIP protein therapeutic that targets the CD37 antigen and has shown potent anti-tumor activity in pre-clinical studies. Trubion initiated a Phase 1 / 2 clinical trial of TRU-016 in March 2008. The open-label clinical trial has two components: a Phase 1 dose escalation study designed to evaluate the safety, tolerability and pharmacokinetics of TRU-016, and a Phase 2 expansion cohort designed to further evaluate safety and estimate clinical activity of TRU-016 in patients with previously treated CLL or SLL.

About Trubion

Trubion is a biopharmaceutical company that is creating a pipeline of novel protein therapeutic product candidates to treat autoimmune and inflammatory diseases and cancer. The Company’s mission is to develop a variety of first-in-class and best-in-class product candidates, customized for optimal safety, efficacy and convenience that it believes may offer improved patient experiences. Trubion’s current product candidates are novel single-chain protein, or SMIP(TM), therapeutics, and are designed using its custom drug assembly technology. Trubion’s product pipeline includes CD20-directed SMIP therapeutics such as TRU-015 and SBI-087 for autoimmune and inflammatory diseases, developed under the Company’s Wyeth collaboration. Trubion’s product pipeline also includes Trubion’s proprietary product candidate, TRU-016, a novel CD37-targeted therapy for the treatment of B-cell malignancies that is currently in Phase

1 / 2 clinical evaluation. In addition to Trubion’s current clinical stage product pipeline, the Company is also developing additional product candidates that build on its product development experience. More information is available in the investors section of Trubion’s website: http://investors.trubion.com/index.cfm.

Forward-Looking Statements

Certain statements in this release may constitute “forward-looking statements” within the meaning of Section 21E of the Securities Exchange Act of 1934 and Section 27A of the Securities Act of 1933. These statements include, but are not limited to, those related to the Company’s future clinical development programs and the timing thereof, the Company’s future regulatory filings and the timing and outcome thereof. These statements are based on current expectations and assumptions regarding future events and business performance and involve certain risks and uncertainties that could cause actual results to differ materially. These risks include, but are not limited to, risks associated with the clinical advancement of TRU-016, the Company’s Wyeth collaboration, including Wyeth’s control over development timelines, the risks that the Company is unable to advance its clinical development programs and regulatory applications and action at the rate it expects, and such other risks as identified in the Company’s quarterly report on Form 10-Q for the period ended March 31, 2009, and from time to time in other reports filed by Trubion with the U.S. Securities and Exchange Commission. These reports are available on the Investors page of the company’s corporate website at http://www.trubion.com/. Trubion undertakes no duty to update any forward-looking statement to conform the statement to actual results or changes in the Company’s expectations.

Contact:

Jim DeNike

Senior Director, Corporate Communications

Trubion Pharmaceuticals, Inc.

(206) 838-0500

[email protected]

http://www.trubion.com

Waggener Edstrom Worldwide Healthcare

Amy Petty

Senior Account Executive

(617) 576-5788

[email protected]