ICD-O-1 Morphology

Effective 1978 - 1991

ICD-O-2 Morphology

Effective 1992 - 2000

ICD-O-3 Morphology

Effective 2001 and later


for cases diagnosed 1978 and later

Primary Site(s)

Primary site must be bone marrow (C421)

Abstractor Notes

Historically the description for this code has been Acute leukemia, NOS. In the 2008 WHO classification, the definition was 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 leukemias are very rare and nothing substantial is known about their frequency. While anecdotal experience generally considers these leukemias to be of poor prognosis, information is too scanty to make any definitive statements.

Diagnostic Confirmation

This histology can be determined by positive histology (including peripheral blood) with or without genetics and/or immunophenotyping. Review the Definitive Diagnostic Methods, Immunophenotyping and Genetics Data sections below, and the instructions in the Hematopoietic Manual for further guidance on assigning Diagnostic confirmation.


Not Applicable

Module Rule

See abstractor notes

Alternate Names

Acute leukemia, NOS
Acute leukemia of ambiguous lineage, NOS
Undifferentiated leukemia


Acute undifferentiated leukemia expresses no markers that are 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.

Definitive Diagnostic Methods

Bone marrow biopsy
Clinical diagnosis
Peripheral blood smear

Genetics Data



CD34 weakly expressed or positive
CD38 expression
HLA-DR expression
TdT positive


Hematologic Transplant and/or Endocrine Procedures

Transformations to

There are no known transformations

Transformations from

There are no known transformations

Same Primaries

Corresponding ICD-9 Codes

208.0 Acute leukemia of unspecified cell type

Corresponding ICD-10 Codes

C95.0 Acute leukemia of unspecified cell type

Corresponding ICD-10-CM Codes (U.S. only)

C95.0 Acute leukemia of unspecified cell type (effective October 01, 2015)

Signs and Symptoms

Bone or joint pain
Easy bruising or bleeding
Eczema-like skin rash
Night sweats
Pain or feeling of fullness below the ribs
Painless lumps
Shortness of breath

Diagnostic Exams

Blood chemistry studies
Chest x-ray
Cytogenetic analysis
Lumbar puncture
Lymph node biopsy
Molecular testing
Peripheral blood smear

Progression and Transformation


Epidemiology and Mortality



Swerdlow SH, Campo E, Harris NL, Jaffe ES, Pileri SA, Stein H, Thiele J (Eds):
WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues (Revised 4th edition)
IARC: Lyon 2017
Section: Acute leukemias of ambiguous terminology
Pages: 182

International Classification of Diseases for Oncology, Third Edition, Second Revision. Geneva: World Health Organization, 2020.
Section: ICD-O-3.2 (2020) Morphological Codes
Pages: http://www.iacr.com.fr/index.php?option=com_content&view=category&layout=blog&id=100&Itemid=577