Leukemia, NOS

ICD-O-1 Morphology

9800/3: Leukemia, NOS
9802/3: Subacute leukemia, NOS
9803/3: Chronic leukemia, NOS
9804/3: Aleukemic leukemia, NOS
9810/3: Compound leukemia
Effective 1978 - 1991

ICD-O-2 Morphology

9800/3: Leukemia, NOS
9802/3: Subacute leukemia, NOS
9803/3: Chronic leukemia, NOS
9804/3: Aleukemic leukemia, NOS
Effective 1992 - 2000

ICD-O-3 Morphology

9800/3: Leukemia, NOS
Effective 2001 and later


for cases diagnosed 1978 and later

Primary Site(s)

Primary site must be bone marrow (C421)

Abstractor Notes

Leukemia, NOS is a generic neoplasm description. DCO cases or path report only cases may stay in this classification.

In most cases, NOS histology is only the provisional diagnosis; the physician will run further diagnostic procedures and look for various clinical presentations to identify a more specific leukemia. Further review of the medical record should be done to look for immunophenotyping or genetic testing that would lead to a more specific diagnosis. If the information is not available in the medical record, follow-back with the treating physician.

A more specific diagnosis would include acute leukemia, NOS as well as any specific acute or chronic leukemia. 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.

Diagnostic Confirmation

This is a histology for which the Definitive Diagnostic Method does not include Genetics Data or Immunophenotyping, thus Diagnostic Confirmation should never be 3. If genetics and/or immunophenotyping are available, re-review to see if a more specific neoplasm can be coded.


Not Applicable

Module Rule


Alternate Names

Aleukemic leukemia, NOS [OBS]
Chronic leukemia, NOS [OBS]
Subacute leukemia, NOS [OBS]


Leukemia is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation (production by multiplication) of blood cells, usually white blood cells (leukocytes). This is a general term for leukemia (unknown cell type, unknown if acute or chronic).

Definitive Diagnostic Methods


Genetics Data






Transformations to

There are no known transformations

Transformations from

There are no known transformations

Same Primaries

Corresponding ICD-9 Codes

208.9 Unspecified leukemia

Corresponding ICD-10 Codes

C95.9 Leukemia, unspecified

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

C95.1 Chronic leukemia of unspecified cell type (effective October 01, 2015)
C95.9 Leukemia, unspecified (effective October 01, 2015)

Signs and Symptoms


Diagnostic Exams


Progression and Transformation


Epidemiology and Mortality



International Classification of Diseases for Oncology, Third Edition, Second Revision. Geneva: World Health Organization, 2020.
Section: ICD-O-3.2 (2020) Morphological Codes