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YM BioSciences Reports Updated Phase I/II Data for its JAK1/JAK2 Inhibitor CYT387 at ASH 2011

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YM BioSciences Inc. has reported updated results from the ongoing Phase I/II study of its JAK1/JAK2 inhibitor, CYT387, for the treatment of myelofibrosis.

The results are being presented this evening in a poster session at the 53rd Annual Meeting of the American Society of Hematology underway in San Diego, CA.

"In this multicenter study, CYT387 continues to demonstrate a unique ability to render and maintain myelofibrosis patients transfusion independent for clinically-relevant periods, while also producing significant and durable improvements in their splenomegaly and constitutional symptoms," said Dr. Nick Glover, President and CEO of YM BioSciences.

Dr. Glover continued, "In addition, MRI results obtained from a subset of subjects confirm the meaningful improvements in splenomegaly as measured by palpation. Moreover, CYT387 was well tolerated, with dosing up to and exceeding two years."

"While additional assessments and analyses are ongoing across dose levels, 300 mg/day appears to be a safe and effective dosing regimen that warrants further clinical development," added Dr. Glover.

"We look forward to leveraging these data to advance our regulatory strategy and our business development activities with the goal of starting pivotal trials in mid-2012."

Phase I/II Study Updated Results

Study Design
The Core Phase I/II study has completed enrollment of 166 myelofibrosis patients across six study sites. The Core study consists of nine 28-day treatment cycles where CYT387 is orally self-administered, primarily at dosages of 150 mg once-daily (QD), 300 mg QD or 150 mg twice-daily (BID).

Patients who tolerate and benefit from the drug may continue to receive CYT387 beyond the Core study in an Extension phase. While data collection and analysis are ongoing, preliminary safety and efficacy results from this multicenter study are presented below.

Subject Characteristics
The majority of the 166 patients enrolled have Primary Myelofibrosis (65%); 22% have Post-Polycythemia vera and 14% have Post-Essential thrombocythemia. Other patient characteristics include:

• DIPSS-Plus category: Int-1 - 11%; Int-2 - 61%; High - 28%
• JAK2V617F positive: 76%
• Red blood cell transfusion-dependent: 44%
• Palpable splenomegaly >10 cm: 80%

The trial also enrolled patients who had received previous therapies, including other JAK inhibitors (12%) and IMiDs (9%).

Subject Disposition
The median follow-up time for patients in the Core study and Extension phase is 10.4 months (range: 0.8-25.6 months; ongoing). To date, 97% of patients who have completed the Core study have continued into the Extension phase.

During the Core study, 32 patients (19%) have discontinued the study, five for possibly or probably related adverse events, for a current overall retention rate of 81%. The retention rate during the Extension phase is currently 79%.

Anemia Response
Of the 68 patients who were transfusion dependent at baseline, to date 54% have become transfusion independent for a minimum of 12 weeks. The median duration of the transfusion-free period has not yet been reached (range: 82-506 days, ongoing).

More than 25% of subjects who were not receiving transfusions while on study experienced at least a 1 g/dL increase in hemoglobin lasting for more than eight weeks.

Of the 26 patients who were dosed at 300mg QD and were transfusion dependent at baseline, to date 65% have become transfusion independent for a minimum of 12 weeks.

Spleen Response
Of the 142 patients evaluable for spleen response, 31% achieved a response per IWG-MRT. The median duration of spleen response has not yet been reached (range: 55 - 574 days, ongoing).

The median time to spleen response was 15 days (range: 6 - 260 days, ongoing). To date, 49% of patients achieved more than a 50% maximal decrease in spleen size from baseline, with 87% achieving more than a 25% maximal decrease.

Of the 51 patients who were dosed at 300mg QD and were evaluable for spleen response, 33% achieved a response per IWG-MRT. Eleven patients were evaluable for spleen response both by MRI and by palpation.

The response rate was 64% by MRI (defined as a 35% decrease in spleen volume) and 45% by palpation (defined as a 50% decrease in spleen length). The median splenic decrease from baseline at three months was -41% by volume measured by MRI and -45% by length measured by palpation.

The majority of patients reporting constitutional symptoms at baseline demonstrated a Complete Resolution or Marked Improvement of their symptoms, including night sweats, pruritus and bone pain.

Safety Results
CYT387 is well tolerated in myelofibrosis patients for dosing periods up to and exceeding two years. Reported adverse effects include thrombocytopenia; transient, mild dizziness; mild peripheral neuropathy; and abnormalities in liver/pancreas-related laboratory tests. Treatment emergent anemia and neutropenia were rarely reported.

Poster presentation and YM conference call:
The updated results from the Phase I/II study will be presented in a poster session at the 53rd Annual Meeting of the American Society of Hematology. Poster #3849, entitled "Safety and Efficacy of CYT387, a JAK1 and JAK2 Inhibitor for the Treatment of Myelofibrosis", will be presented at Session #634, Myeloproliferative Syndromes: Poster III, being held on Monday, December 12th from 6:00-8:00pm PT in Hall GH of the San Diego Convention Center.