Mycosis fungoides

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)

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

Abstractor Notes

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.

Characteristics of MF:
1. Indolent clinical course with slow progression over years or sometimes decades.
2. Progresses from patches to more infiltrated plaques and eventually tumors.
3. A combination of patches, plaques, and tumors which show ulceration are common. Rarely, patients present with or develop an erythrodermic stage of disease that lack the hematologic criteria of Sezary syndrome.

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


Alternate Names

Folliculotropic MF
Granulomatous slack skin
Ketron-Goodman disease
Kiel: small cell, cerebriform
Lukes-Collins: cerebriform T
Pagetoid reticulosis
Woringer-Kolopp type


Mycosis fungoides is an epidermotropic primary cutaneous T-cell lymphoma characterized by infiltrates of small to medium-sized T lymphocytes with cerebriform nuclei. The term mycosis fungoides should be used only for classic cases, characterized by the evolution of patches, plaques, and tumors, or for variants with a similar clinical course.

There are three variants to MF

1. Folliculotropic mycosis fungoides is characterized by infiltrates of atypical (cerebriform) CD4+ T lymphocytes involving hair follicles, often with sparing of the epidermis. Many cases show mucinous degeneration of the hair follicles (follicular mucinosis), but mucin deposition can be absent. The lesions preferentially involve the head and neck area and often present with grouped follicular papules and plaques associated with alopecia.

2. Pagetoid reticulosis is characterized by patches or plaques with an intraepidermal proliferation of neoplastic T cells. The term should only be used for the localized type. The atypical cells have medium-sized or large cerebriform nuclei and either a CD4-/CD8+ phenotype or (less commonly) or CD4+/CD8- phenotype.

3. Granulomatosis slack skin is an extremely rare subtype of cutaneous T-cell lymphoma characterized clinically by the development of bulky, pendulous skin folds in the flexural areas (axilla, groin) and histologically by a granulomatosis infiltrate with the dermis and subcutaneous tissues, with clonal CD4+ T cells, abundant macrophages with many multinucleated giant cells, and loss of elastic fibers.

Definitive Diagnostic Methods

Genetic testing
Histologic confirmation

Genetics Data

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


CD2 positive
CD3 positive
CD4 positive
CD4- Pagetoid reticulosis
CD5 positive
CD7 negative
CD8 positive or negative
CD30 expression
CD56 expression
TCR beta positive


Hormone therapy
Other therapy
Radiation therapy

Transformations to

There are no known transformations

Transformations from

There are no known transformations

Corresponding ICD-9 Codes

202.1 Mycosis fungoides

Corresponding ICD-10 Codes

C84.0 Mycosis fungoides

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

C84.0 Mycosis fungoides (effective October 01, 2015)

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

Progression and Transformation


Epidemiology and Mortality

Age: mostly elderly, although can occur in children and adolescents
Incidence: 50% of all cutaneous lymphomas
Survival: patients with limited disease have excellent prognosis; those with extensive disease have a poor prognosis


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 T- and NK-cell neoplasms
Pages: 385-389

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

National Cancer Institute
Section: General Information About Mycosis Fungoides (Including S├ęzary Syndrome) Treatment