NEW YORK (TheStreet) -- Investors appear concerned about Pharmacyclics' (PCYC) leukemia drug Imbruvica relative to the competing drug ABT-199 under development by Abbvie (ABBV). ABT-199 is an exceptionally active drug and will have a significant role in the treatment of chronic lymphocytic leukemia, but I find data in the just-released ASCO abstracts to be more positive for Pharmacyclics and Imbruvica than its competition.
While many have focused on Imbruvica monotherapy data with a treatment that is efficacious, safe, and easy to use for both the patient and doctor, I was more intrigued by data from the combination therapy of Imbruvica and GlaxoSmithKline's (GSK) Arzerra (an anti-CD20 antibody.) While the clinical trial was small, just over 70 total patients, it tested three dosing regimens of the Imbruvica-Arzerra combination with overall response rates ranging from 71% to 100%. These results are significant because they help blunt ABT-199's efficacy advantage over Imbruvica, which in turn, makes Imbruvica's safety advantage over ABT-199 more meaningful.
ABT-199 as a monotherapy is generating overall response rates around 78% in CLL, which one could argue is marginally better than Imbruvica, although at the expense of decreased tolerability. In addition, ABT-199 also has a small trial with Rituxan (also an anti-CD20 antibody) which generated an overall response rate of 78%. The depth of responses in this combination study were impressive, with 39% of patients achieving a complete response. Five of the six complete responses were minimal residual disease (MRD) negative, which is seen as potentially curative. With these ASCO data, it's easy to see why ABT-199 is deemed a threat to Imbruvica.