NeoRx's Skeletal Targeted Radiotherapy - STR - Completes Phase II Testing.

Business Editors

SEATTLE--(BUSINESS WIRE)--Feb. 23, 2000

-- Excellent safety profile at highest doses

reinforces Phase I results --

NeoRx Corporation (Nasdaq:NERX) presenting at the Cruttendon Roth conference in Laguna Niguel, CA said excellent safety was observed in the Phase II study of its Skeletal Targeted Radiotherapy (STR) against multiple myeloma, a fatal cancer arising in the bone. Once a patient has been treated, safety data is available in approximately thirty days; efficacy data is available approximately six months after therapy is administered.

"The excellent safety profile observed in the Phase I dose escalation part of the study has been confirmed in these Phase II patients treated at the highest dose with which we expect to conduct the pivotal trial," said Paul G. Abrams, M.D., J.D., NeoRx's Chief Executive Officer. "This, plus the encouraging number of complete remissions observed in Phase I, has led us to schedule a meeting with FDA to discuss our Phase III protocol design, to sign up PPD, Inc. as our Clinical Research Organization (CRO) for the study, with whom we have also obtained a creative financing vehicle, and to engage International Isotopes, Inc. to build a Phase III trial manufacturing facility."

Fourteen patients received 40 Gray (4000 rads) of radiation; nearly four times the highest dose generally administered with conventional external beam radiation therapy, in addition to standard high-dose chemotherapy. No toxicity above Grade II in organs other than bone marrow was encountered in the thirteen Phase II patients treated last year; the 14th was treated more recently and awaits evaluation. The excellent safety profile prompted the investigators to raise the age limits of patients for inclusion in the pending Phase III trial slated to begin in the second or third quarter of this year.

Last December at the American Society of Hematology meetings, Dr. Richard Champlin, Head of the Leukemia and Lymphoma Transplant Section at MD Anderson Hospital (Houston, TX) and a principal investigator on the study, reported 12 of 27 patients evaluated in Phase I had achieved complete remission, defined by the absence of myeloma tumor cells in the bone marrow and the absence of the characteristic myeloma protein in the blood and urine by the most stringent biochemical tests currently in common use.

STR consists of holmium-166, a radionuclide, linked to a drug that has a homing mechanism for bone. Studies have indicated that the therapy targets bone, especially areas surrounding tumors in the bone. STR was administered at 40 Gray (or 4000 rads) to the bone marrow, along with standard high dose chemotherapy with melphalan.

There are approximately 15,000 new patients with multiple myeloma annually in North America. STR has received Orphan Drug Status from the FDA.

This release contains forward-looking statements relating to the development of the Company's products and future operating results that are subject to certain risks and uncertainties that could cause actual results to differ materially from those projected. The words "believe," "expect," "intend," "anticipate," variations of such words, and similar expressions identify forward-looking statements, but their absence does not mean that a statement is not forward-looking. These statements are not guarantees of future performance and are subject to certain risks, uncertainties and assumptions that are difficult to predict. Factors that could affect the Company's actual results include the progress and costs of clinical trials and the timing of regulatory approvals. Reference is made to the Company's latest Annual Report on Form 10 - K filed with the Securities and Exchange Commission for a more detailed description of such factors. Readers are cautioned not to place undue reliance on these forward-looking statements that speak only as of the date of this release. The Company undertakes no obligation to publicly update any forward-looking statement to reflect new information, events or circumstances after the date of this release or to reflect the occurrence of unanticipated events.

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