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9 - Grade/differentiation unknown, not stated, or not applicable
Acute leukemia, NOS
Blast cell leukemia
Hybrid acute leukemia
Stem cell acute leukemia
Stem cell leukemia
Acute undifferentiated leukemia expresses no markers considered specific for either lymphoid or myeloid lineage. Before categorizing a leukemia as undifferentiated, it is necessary to perform immunophenotyping with a comprehensive panel of monoclonal antibodies in order to exclude leukemias of unusual lineages, such as those derived from myeloid or plasmacytoid dendritic cell precursors, NK-cell precursors, basophils or even non-hematopoietic tumors.
Historically the description for this code has been Acute leukemia, NOS. In the new WHO classification the definition has been changed to acute undifferentiated leukemia.
Acute leukemia NOS is a generic disease description. DCO cases or path report only cases may stay in this classification. In most cases, leukemia, NOS is only the provisional diagnosis; the physician will run further diagnostic procedures and look for various clinical presentations to identify a more specific disease. Further review of the medical record should be done to look for the tests listed as definitive diagnosis. If no information is found on the medical record, follow-back with the attending physician must be done. The more specific leukemias are any of the specific acute leukemias. When a more specific diagnosis is identified, the histology should be changed to the more specific neoplasm name and code. See the histology tables for more information on NOS and more specific histologies.
Acute undifferentiated leukemia affects the bone marrow and peripheral blood. There are too few cases to know whether there is a predilection for other sites. These lymphomas are very rare and nothing substantial is known aabout their frequency. While anecdotal experience generally considers these leukemias to be of poor prognosis, information is too scanty to make any definitive statements.