Leukemia, NOS

ICD-O-1 Morphology
9800/3: Leukemia, NOS
Effective 1978 - 1991
ICD-O-2 Morphology
9800/3: 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)

Code grade specified by pathologist. If no grade specified, code 9
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).
Abstractor Notes
Leukemia, NOS is a generic disease 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.
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)
C95.9 Leukemia, unspecified (effective October 01, 2015)
C95.1 Chronic leukemia of unspecified cell type (effective October 01, 2015)
Signs and Symptoms
Diagnostic Exams
Progression and Transformation
Epidemiology and Mortality