AbbVie Inc. said its medicine venetoclax helped slow down the progression of a type of blood cancer when combined with Roche Holding AG's Rituxan.

The North Chicago, Ill.-based pharmaceutical giant is studying the combination in a phase 3 trial dubbed Murano in patients with chronic lymphocytic leukemia who did not respond to existing treatment or whose disease returned.

Chronic lymphocytic leukemia, or CLL, is a type of cancer in which the bone marrow produces too many white blood cells.

Of the 389 patients enrolled in the study, 121 patients achieved undetectable minimal residual disease, meaning less than one cancer cell out of 10,000 white blood cells. Of these 121 patients, 83% did not see their disease worsen for an average of 13.8 months.

Venetoclax, which is marketed as Venclyxto, is approved in the U.S. for CLL patients with a specific chromosomal abnormality. The European Medicines Agency had also previously recommended the drug for approval in the same indication.

AbbVie jointly markets the medicine with Roche's unit Genentech Inc. in the U.S., and on its own outside America.