Lymphoblasts are immature cells which typically differentiate

Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a simple zygote to a complex system of...

 to form mature lymphocyte

Lymphocyte

A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...

s. Normally lymphoblasts are found in the bone marrow, but in acute lymphoblastic leukemia

Acute lymphoblastic leukemia

Acute lymphoblastic leukemia is a form of leukemia, or cancer of the white blood cells characterized by excess lymphoblasts.Malignant, immature white blood cells continuously multiply and are overproduced in the bone marrow. ALL causes damage and death by crowding out normal cells in the bone...

 (ALL), lymphoblasts proliferate uncontrollably and are found in large numbers in the peripheral blood.

The size is between 10 and 20 μm.

Although commonly lymphoblast refers to a precursor cell in the maturation of leukocytes, the usage of this term is sometimes inconsistent. The Chronic Lymphocytic Leukemia Research Consortium defines a lymphoblast as "A lymphocyte that has become larger after being stimulated by an antigen. Lymphoblasts look like immature lymphocytes, and were once thought to be precursor cells.". Commonly, when speaking about leukemia, "blast" is used as an abbreviation for lymphoblasts.

Lymphoblasts can be distinguished microscopically from myeloblast

Myeloblast

The myeloblast is a unipotent stem cell, which will differentiate into one of the actors of the Granulocyte series.- Origin :These cells descend from the primitive reticulum cells, which are found in the stroma of the marrow. There is also an intermediate phase between the myeloblast and these...

s by having fewer nucleoli than do myeloblasts, and the nuclear chromatin is more condensed, and cytoplasmic granules are absent.