This neoplasm is not reportable.


Monoclonal B-cell lymphocytosis, CLL-type

ICD-O-3 Morphology

9823/1: Monoclonal B-cell lymphocytosis, CLL-type
Effective 2021 and later


This neoplasm is not reportable

Primary Site(s)

No primary site specified
This neoplasm is reportable for primary sites C700-C729, C751-C753 only.

Alternate Names

MBL, atypical CLL-type
MBL, chronic lymphocytic leukemia (CLL)-type
MBL, CLL-type
Monoclonal B lymphocytosis of uncertain significance


Monoclonal B-cell lymphocytosis (MBL) is defined by a monoclonal B-cell count < 5 x 10 to the ninth/L in the peripheral blood in subjects who have no associated lymphadenopathy, organomegaly, other extramedullary involvement, or any other feature of a B-cell lymphoproliferative disorder.

MBL is classified into three categories on the basis of phenotype
1) MBL, atypical CLL-type
2) MBL, chronic lymphocytic leukemia (CLL)-type
3) MBL, non-CLL type (see 9591/1)

Corresponding ICD-9 Codes

288.61 Lymphocytosis (symptomatic)

Corresponding ICD-10 Codes

D72.8 Other specified disorders of white blood cells

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

D72.820 Lymphocytosis (symptomatic) (effective October 01, 2015)


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: Mature B-cell neoplasms
Pages: 220-221

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