Search Database ICD-O-3 Code Lists

Name

Mycosis fungoides (MF)

ICD-O-3 Morphology

9700/3: Mycosis Fungoides
Effective 2001 and later

Reportable

for cases diagnosed 1978 and later

Primary Site(s)

C440-C449 , C510-C512 , C518-C519 , C600-C602 , C608-C609 , C632
Cutaneous (skin) lymphoma which presents with generalized skin lesions.

Assign C449 if specific primary site cannot be determined.

See abstractor notes

Coding Manual: Hematopoietic Coding Manual (PDF)

Abstractor Notes

Mycosis fungoides (MF) is part of the Mature T-cell and NK-cell neoplasms lineage table in the WHO 5th edition of Hematolymphoid Tumors. (See Appendix B in the Hematopoietic Manual, Table B20)

Mycosis fungoides (MF) as a rule is limited to the skin with widespread distribution for a protracted period. Extracutaneous disease may occur in advanced stages to lymph nodes, liver, spleen, lungs, and blood.

Large-cell transformation of Mycosis Fungoides is the same primary. This diagnosis is associated with disease progression.

There are several subtypes

Classic Mycosis Fungoides
Skin lesions of MF can be one or few, localized or multiple and widespread, and sometimes even confluent. When localized, the lesions often occur in sun-protected areas, like skin flexures (axillae, groins) and the lower trunk / buttocks (bathing-trunk distribution).

Extracutaneous dissemination occurs exclusively in the latest stages of disease, initially involving the draining lymph nodes, and occasionally spreading more extensively to the viscera and blood.

Folliculotropic mycosis fungoides
Refers to cases of MF with or without adnexal involvement beyond the hair follicles, which may occasionally present as predominantly syringotropic MF. It arises most commonly on the head and neck, upper extremities, and thorax.

Pagetoid reticulosis (Woringer-Kolopp type)
Slow growing, well-circumscribed solitary psoriasiform or keratotic plaque (or plaques) affecting the distal extremities or trunk, occurring in all ages.

Granulomatosis slack skin
Exceedingly rare, presents with pendulous skin in the axillae, groin, and gluteal folds, with pruritis, erythema, and patches and plaques in skin segments.

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.

Module Rule

None

Alternate Names

Adnexotropic (folliculotropic and/or syringotropic) mycosis fungoides
Hypopigmented mycosis fungoides
Pagetoid reticulosis (Woringer-Kolopp type)

Definition

Mycosis fungoides (MF) is a primary cutaneous T-cell lymphoma clinically characterized by the sequential evolution of patches, plaques, and tumours, and pathologically comprising infiltrates of clonal small to medium-sized mature T cells with hyperconvoluted nuclei, which are epitheliotropic in most cases. (WHO 5th edition)

Definitive Diagnostic Methods

Clinical diagnosis
Cytogenetics
Genetic testing
Histologic confirmation
Immunohistochemistry
Immunophenotyping

Genetics Data

CDKN2A (p16INK4a and PTEN) inactivation
TR genes are clonally rearranged
STAT3 activation

Immunophenotyping

CD2+ (expression/positive)
CD3+ (expression/positive)
CD4+ (expression/positive)
CD4- (no expression/negative)
CD5+ (expression/positive)
CD7- (no expression/negative)
CD8- (no expression/negative)
CD30+ (expression/positive)
CD56+ (expression/positive)
TCRB+ (expression/positive)

Treatments

Chemotherapy
Hormone therapy
Immunotherapy
Other therapy
Radiation therapy
Surgery

Transformations to

There are no known transformations

Transformations from

There are no known transformations

Same Primaries

Corresponding ICD-10 Codes (Cause of Death codes only)

C84.0 Mycosis fungoides

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

C84.0_ Mycosis fungoides (effective October 01, 2015)
C84.0A Mycosis fungoides, in remission (effective October 01, 2024)

Signs and Symptoms

Itchy, painful, peeling and reddened skin
Skin lesions: papules, patches, plaques or tumors
Ulcerated skin lesions, which may become infected

Diagnostic Exams

Flow cytometry
Immunophenotyping
Peripheral blood smear
Skin biopsy
T-cell receptor (TCR) gene arrangement test

Progression and Transformation

None

Epidemiology and Mortality

Incidence: 50% of all cutaneous lymphomas, 5.8 cases per 1 million person years
Age: can occur at any age, peak incidence late 50's
Sex: M:F ratio 2:1
Survival: patients with limited disease have excellent prognosis; those with extensive disease have a poor prognosis

Sources

WHO Classification of Tumours Editorial Board. Haematolymphoid tumours. Lyon (France): International Agency for Research on Cancer; 2024. (WHO classification of tumours series, 5th ed.; vol. 11). https://publications.iarc.who.int/637.
Section: Mature T-cell and NK-cell neoplasms
Pages: Part B: 688-693

International Classification of Diseases for Oncology, 3rd edition (including revisions). Geneva: World Health Organization, 2001, 2011, 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

PDQ® Adult Treatment Editorial Board. PDQ Mycosis Fungoides and Other Cutaneous T-Cell Lymphomas Treatment. Bethesda, MD: National Cancer Institute. Updated <02/19/2025>. Available at: https://www.cancer.gov/types/lymphoma/hp/mycosis-fungoides-treatment-pdq. Accessed <03/31/2025>. [PMID: 2638928
Section: Mycosis Fungoides and Other Cutaneous T-Cell Lymphomas Treatment (PDQ®)–Health Professional Version
Pages: https://www.cancer.gov/types/lymphoma/hp/mycosis-fungoides-treatment-pdq
Glossary