Clonal culture and cytogenetics. Indicators of a variant of chronic myelogenous leukemia.

The clonal growth pattern of bone marrow and peripheral blood cells from 16 patients with clinically suspected chronic myelogenous leukemia (CML) was evaluated in the double-layer agar system. Cytogenetic studies were performed on parallel marrow and peripheral blood samples. In four cases a unique growth pattern emerged, characterized by normal or increased colony-forming units (CFUc), and markedly elevated cluster-forming units (CIFUc). Three of these were Philadelphia chromosome (Ph1)-negative (atypical CML) and the fourth showed a mixture of Ph1-positive and chromosomally normal cells (Ph1-negative). Of the remaining cases, five proved to be CML Ph1-positive with progression to blast crisis on the basis of clinical data, clonal culture, and cytogenetics, and seven proved to be disorders other than myeloid leukemia. The combined results from clonal growth and cytogenetics have added a new parameter in the diagnosis of atypical CML and may aid in the earlier diagnosis and treatment of patients with this CML variant.