Geron's Imetelstat Data in Myelofibrosis: 4 CRs, 1 PR. But Are These Responses Real? (Update)

We just got a first look at results from a Mayo Clinic study of Geron's (GERN) imetelstat in myelofibrosis. The stock doubled at Thursday's open but has since sold off some, now up 61% to $5.80. 

The headline: 4 patients had complete remission (CR), 1 patient had a partial remission (PR) and 3 patients showed clinical improvement (CI). This is out of 18 patients evaluable for response -- 11 from the first Cohort A and 7 from Cohort B. 

But (uh oh) are these imetelstat CRs and PRs real? Maybe not so much. Maybe an exaggeration. I'll explain below, but first here's the text of the research abstract just released:

Background: JAK inhibitors, including ruxolitinib, are to date incapable of inducing complete (CR) or partial (PR) remissions, reversal of bone marrow (BM) fibrosis or molecular responses in myelofibrosis (MF). This is consistent with the fact that JAK2 mutations are neither specific nor pathogenetically essential for the disease. Other currently available drugs in MF are equally ineffective in terms of disease-modifying activity.

Methods: In an investigator-sponsored single-center study (ClinicalTrials.gov Identifier: NCT01731951), imetelstat, a lipid-conjugated oligonucleotide inhibitor of human telomerase, was administered to patients with high or intermediate-2 risk MF (JCO 2011). Adverse events were monitored by common terminology criteria (Version 4.03) and responses by the International Working Group criteria (Blood 2013). Eligibility criteria included platelets ≥50 x 10(9)/L. Study drug and funding were provided by Geron Corporation (Menlo Park, CA, USA).

Imetelstat was administered by a 2-hour intravenous infusion (9.4 mg/kg) every three weeks (cohort A) or weekly x 3 followed by every three weeks (cohort B). Mutations with prognostic (ASXL1 and SRSF2) or phenotypic (SF3B1 and U2AF1) relevance were screened by DNA sequencing. Quantitative PCR was used to measure JAK2V617F burden (assay sensitivity 0.01%). Laboratory correlative studies included analyses of granulocyte telomere length, mononuclear cell telomerase activity and human telomerase reverse transcriptase (hTERT) isoforms.

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