lymphoblastic leukemia

n.
  1. A type of lymphocytic leukemia characterized by abnormal, often immature, lymphocytic cells or by the presence of unusually large numbers of immature lymphocytes occurring together with adult lymphocytes.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.