undifferentiated

adj. not differentiated

Stem cells are primal cells found in all multi-cellular organisms. They retain the ability to renew themselves through mitotic cell division and can differentiate into a diverse range of specialized cell types. Research in the human stem cell field grew out of findings by Canadian scientists Ernest A. McCulloch and James E. Till in the 1960s.
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Adjective
1. not differentiated
(synonym) uniform
(antonym) differentiated
(similar) dedifferentiated

(a.)
Not differentiated; specifically (Biol.), homogenous, or nearly so; -- said especially of young or embryonic tissues which have not yet undergone differentiation (see Differentiation, 3), that is, which show no visible separation into their different structural parts.
  

A term used to describe cells or tissues that do not have specialized ("mature") structures or functions. Undifferentiated cancer cells often grow and spread quickly.