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Skin nonmelanocytic tumor

General

WHO classification

Authors: Chico J. Collie, M.B.B.S., Jonathan D. Ho, M.B.B.S., D.Sc.

Editorial Board Member: Bethany R. Rohr, M.D.

Last author update: 20 September 2023

Last staff update: 26 February 2024

Copyright: 2023-2025, PathologyOutlines.com, Inc.

PubMed Search: Skin nonmelanocytic tumor WHO

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Table of Contents

Cite this page: Collie CJ, Ho JD. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnonmelanocyticWHO.html. Accessed March 31st, 2025.

Definition / general

WHO classification of nonmelanocytic skin tumors

Major updates

Epidermal tumors
- Keratoacanthoma (KA) is kept separate from squamous cell carcinoma (SCC), while recognizing it may be a well differentiated SCC with self resolving tendencies
- Merkel cell carcinoma is now classified as a neuroendocrine carcinoma of the skin
Appendageal tumors
- Genetic tumor syndromes associated with skin malignancies chapter discusses adnexal tumor syndromes in depth
- New molecular aberrations in nonsyndromic appendageal tumors added
- Cribriform carcinoma renamed cribriform tumor
- Oncogenic HPV42 present in digital papillary adenocarcinoma
- Addition of (provisional) entity: primary adnexal NUT carcinoma added
Tumors of nail unit added
Hematolymphoid tumors
- New insights into the molecular pathophysiology and response to targeted therapy
- Updates for histiocytic / dendritic cell neoplasms (ALK and BRAF mutation drivers)
- Cutaneous peripheral T cell lymphomas listed separately
- Cutaneous peripheral T cell lymphoma, NOS is applied to cases not falling within a specific category
- Section on primary immunodeficiency associated lymphoproliferative disorders added
- Reinclusion of reactive lymphoid hyperplasia (last covered in 3rd edition)
Soft tissue tumors
- Introduction of 4 new entities
  - CRTC1::TRIM11 cutaneous tumor
  - Superficial CD34+ fibroblastic tumor (PRDM10 rearranged soft tissue tumor)
  - EWSR1::SMAD3 rearranged fibroblastic tumor
  - NTRK rearranged spindle cell neoplasm
- Atypical intradermal smooth muscle neoplasm preferred terminology for dermal leiomyosarcoma
- Reclassification of epithelioid fibrous histiocytoma in family of tumors of uncertain differentiation
Skin metastasis
- Known tumors metastasizing to skin
- Carcinoma, unknown primary

WHO (2022)

Keratinocytic / epidermal tumors

ICD-O

ICD-11

Carcinoma precursors and benign simulants
- Premalignant keratoses and precursors
  - Actinic keratosis
    8070/0
    EK90.0
  - Arsenical keratosis
    8070/0
    EK90.Y & XH5NG4
  - PUVA keratosis
    8070/0
    EK90.Y & XH5NG4
  - Squamous cell carcinoma in situ (Bowen disease)
    8070/2
    2E64.00
- Verrucae
  - Verruca vulgaris
    None
    1E80
  - Verruca plantaris and palmaris
    None
    1E80.1
  - Verruca plana
    None
    1E80.1
- Benign acanthomas / keratoses
  - Seborrheic keratosis
    8052/0
    2F21.0
  - Solar lentigo
    8052/0
    EJ20.1 & XH7B58
  - Lichen planus-like keratosis
    8052/0
    2F21.Y & XH63L8
  - Clear cell acanthoma
    8084/0
    2F21.Y & XH13L5
  - Large cell acanthoma
    8072/0 & 8052/0
    2F21.Y & XH7AQ2
  - Warty dyskeratoma
    8054/0
    2F21.Y & XH65S7
  - Other benign keratoses
    8052/0
    2F21.Y
    - Acantholytic acanthoma
    - Acantholytic dyskeratotic acanthoma
    - Epidermolytic acanthoma
    - Granular parakeratotic acanthoma
    - Psoriasiform keratosis
    - Melanoacanthoma
Epidermal carcinomas
- Basal cell carcinomas
  8090/3
  2C32.Z
  - Superficial basal cell carcinoma
    8091/3
    2C32.2
  - Nodular basal cell carcinoma
    8097/3
    2C32.0
  - Micronodular basal cell carcinoma
    8097/3
    2C32.Y & XH4GJ2
  - Infiltrating basal cell carcinoma
    8092/3
    2C32.Y & XH5VK4
  - Sclerosing / morphoeic basal cell carcinoma
    8092/3
    2C32.1
  - Basosquamous carcinoma
    8094/3
    2C32.Y & XH4C18
  - Basal cell carcinoma with sarcomatoid differentiation
    8092/3
    2C32.Y & XH1JH6
  - Basal cell carcinoma with adnexal differentiation
    8090/3
    2C32.Y & XH6S67
  - Fibroepithelial basal cell carcinoma
    8093/3
    2C32.Y & XH45F3
- Keratoacanthomas
  - Keratoacanthoma
    8071/3
    2C31.1
    - Giant keratoacanthoma
    - Keratoacanthoma centrifugum marginatum
    - Multiple keratoacanthoma-like proliferations and eruptive squamous atypia
    - Keratoacanthoma in Muir-Torre syndrome
    - Multiple self healing epitheliomas of Ferguson-Smith
    - Generalized eruptive keratoacanthoma of Grzybowski
- Squamous cell carcinomas
  8070/3
  2C31.Z
  - Verrucous squamous cell carcinoma
    8051/3
    2C31.0
  - Acantholytic squamous cell carcinoma
    8075/3
    2C31.Z & XH7LH0
  - Lymphoepithelial carcinoma
    8082/3
    2C31.Z & XH1E40
  - Clear cell squamous cell carcinoma
    8084/3
    2C31.Z & XH9DC1
  - Spindle cell squamous cell carcinoma
    8074/3
    2C31.Z & XH6D80
  - Squamous cell carcinoma with sarcomatoid differentiation
    8074/3
    2C31.Z & XH6D80
Neuroendocrine neoplasms
- Neuroendocrine carcinomas
  - Merkel cell carcinoma
    8247/3
    2C34 & XH81N8
    - Merkel cell polyomavirus positive versus negative
    - Pure versus combined (most commonly with squamous cell carcinoma)

Appendageal tumors

ICD-O

ICD-11

Tumors with apocrine and eccrine differentiation
- Benign apocrine and eccrine tumors
  - Hidrocystoma / cystadenoma
    8404/0
    EK70.3, 2F3Z & XH5RJ2
  - Syringoma
    8407/0
    2F22 & XH6325
  - Poroma
    8409/0
    2F22 & XH8N28
    - Hidroacanthoma simplex
    - Classic poroma
    - Dermal duct tumor and poroid hidradenoma
  - Syringofibroadenoma
    8392/0
    2F22 & XH06Y5
  - Hidradenoma
    8402/0
    2F22 & XH4MV7
  - Spiradenoma
    8403/0
    2F22 & XH3AM1
  - Cylindroma
    8200/0
    2F22, XH6J91, 2F22 & XH5GN1
  - Tubular adenoma
    8211/0
    2F22 & XH7SY6
  - Syringocystadenoma papilliferum
    8406/0
    2F22 & XH1PY0
  - Mixed tumor
    8940/0
    2F22 & XH70N8
    - Apocrine
    - Eccrine
  - Myoepithelioma
    8982/0
    2F7C & XH3CQ8
    - Syncytial myoepithelioma
    - Myoepithelial carcinoma
- Malignant apocrine and eccrine tumors
  - Adnexal adenocarcinoma, NOS
    8390/3
    2C33 & XH89V4
  - Microcystic adnexal carcinoma
    8407/3
    2C33 & XH17P2
  - Cribriform tumor (previously carcinoma)
    8201/3
    2C33 & XH1YZ3
  - Porocarcinoma
    8409/3 (invasive)
    8409/2 (in situ)
    2C33, XH7WE6, 2C33 & XH7VK4
  - NUT carcinoma
    8023/3
    2D42 & XH2855
  - Malignant neoplasms arising from spiradenoma, cylindroma
    8403/3
    2C33 & XH2ZK9 (ex cylindroma)
    
    or spiradenocylindroma
    2C33 & XH9C82 (ex spiradenoma)
    
    2C33 & XH9NW9 (ex spiradenocylindroma)
  - Malignant mixed tumor
    8940/3
    2C33 & XH0V86
  - Hidradenocarcinoma
    8402/3
    2C33 & XH7NK9
  - Endocrine mucin producing sweat gland carcinoma
    8509/3
    2C33 & XH4EK4
  - Mucinous carcinoma
    8480/3
    2C33 & XH1S75
  - Digital papillary adenocarcinoma
    8408/3
    2C33 & XH6FB5
  - Adenoid cystic carcinoma
    8200/3
    2C33 & XH4302
  - Apocrine carcinoma
    8401/3
    2C33 & XH9L77
  - Squamoid ductal eccrine carcinoma
    8560/3
    2C33 & XH95Y6
  - Syringocystadenocarcinoma papilliferum
    8406/3
    2C33 & XH0BE5
  - Secretory carcinoma
    8502/3
    2C33 & XH44J4
  - Signet ring cell / histiocytoid carcinoma
    8490/3
    2C33 & XH0XE5
Tumors with follicular differentiation
- Benign tumors with follicular differentiation
  - Trichoblastoma
    8100/0
    2F22 & XH2K97
  - Pilomatricoma
    8110/0
    2F22 & XH9E37
  - Melanocytic matricoma
    8110/0
    2F22 & XH7CM2
  - Trichilemmoma
    8102/0
    2F22 & XH5AU2
  - Trichoadenoma
    8391/0
    2F22
  - Trichofolliculoma
    8104/0
    2F22 & XH0U05
  - Pilar sheath acanthoma
    8104/0
    2F22 & XH3EY8
  - Tumor of the follicular infundibulum
    8104/0
    2F22 & XH0489
  - Trichodiscomas and fibrofolliculomas
    8391/0
    2F22 & XH4YU8
- Malignant tumors with follicular differentiation
  - Proliferating trichilemmal tumor
    8103/1
    2C33 & XH7WJ7
    - Benign proliferating trichilemmal tumor
    - Atypical (intermediate) proliferating trichilemmal tumor
    - Malignant proliferating trichilemmal tumor
  - Pilomatrical carcinoma
    8110/3 or 8980/3 (carcinosarcoma)
    2C33 & XH9G49/XH8324 (carcinosarcoma)
  - Trichoblastic carcinoma / carcinosarcoma
    8100/3
    2C33 & XH3DL9
  - Trichilemmal carcinoma
Tumors with sebaceous differentiation
- Benign tumors with sebaceous differentiation
  - Sebaceoma
    8410/0
    2F22 & XH0QL4
  - Sebaceous adenoma
    8410/0
    2F22 & XH1NC5
- Malignant tumors with sebaceous differentiation
  - Sebaceous carcinoma
    8410/3
    2C33 & XH4VR2
Site specific appendageal tumors
- Benign site specific appendageal tumors
  - Hidradenoma papilliferum
    8405/0
    2F22 & XH4DX4
  - Fibroadenoma and phyllodes tumor of anogenital
    9010/0 (fibroadenoma, NOS)
    9020/0 (phyllodes tumor)
    2F33.Y & XH9HE2 (fibroadenoma)
    2F33.Y & XH50P7 (phyllodes tumor)
    
    mammary-like glands
- Malignant site specific appendageal tumors
  - Mammary Paget disease
    8540/3
    2E65.5 & XH3E21
  - Extramammary Paget disease
    8542/3
    2E64.1 or 2E67.11 or 2C81.Y & XH70F8
  - Adenocarcinoma of mammary gland type
    8500/3
    2C70.Z & XH9FX2

Tumors of the nail unit

ICD-O

ICD-11

Nail bed epithelial tumors
- Onychomatricoma
  8110/0
  2F2Y
  - Pleomorphic
  - Pigmented
  - Myxoid
  - Proliferative
- Onychopapilloma
  8052/0
  2F2Y
- Ungual fibrokeratoma
  8052/0
  2F23.Y
- Onychocytic matricoma
  8052/0
  2F2Y
- Subungual keratoacanthoma
  8071/3
  2C31.1
  - Subungual tumor of incontinentia pigmenti

Tumors of hematopoietic and lymphoid origin

ICD-O

ICD-11

Myeloid proliferations and neoplasms
- Mastocytosis
  - Mastocytosis
    9740/1
    2A21.Z
  - Mast cell sarcoma
    9740/3
    2A21.2
- Secondary cutaneous involvement in myeloid neoplasms
  - Cutaneous involvement in myeloid neoplasms, including
    9930/3
    2A60.39
    
    myeloid sarcoma
Histiocytic or dendritic cell neoplasms
- Plasmacytoid dendritic cell neoplasms
  - Mature plasmacytoid dendritic cell proliferation associated with myeloid neoplasm
  - Blastic plasmacytoid dendritic cell neoplasm
    9727/3
    2A60.5
- Langerhans cell neoplasms
  - Langerhans cell histiocytosis
    9751/1
    2B31.2
- Histiocytic tumors
  - Xanthelasma
    
    9A06.4
  - Juvenile xanthogranuloma
    9749/1
    2B31.0
  - Reticulohistiocytosis
    8831/0
    EE8Y
  - Rosai-Dorfman disease
    9749/3
    EK92
  - Erdheim-Chester disease
    9749/3
    2B31.Y & XH1VJ3
  - ALK+ histiocytosis
    9750/3
    EK92
  - Histiocytic sarcoma
    9755/3
    2B31.1
- Other dendritic cell neoplasms
  - Indeterminate dendritic cell tumor
    9757/3
    2B31.6
Cutaneous B cell lymphoproliferative disorders and neoplasms
- Reactive B cell rich lymphoid proliferations
  
  4B07
- Primary cutaneous mature B cell neoplasms
  - Primary cutaneous marginal zone lymphoma
    9699/3
    2A85.2
  - Primary cutaneous follicle center lymphoma
    9597/3
    2A80.3
  - Primary cutaneous diffuse large B cell lymphoma, leg type
    9680/3
    2A81.A
  - Intravascular large B cell lymphoma
    9712/3
    2A81.1
- Cutaneous involvement in primarily extracutaneous B cell lymphomas and leukemias
  - Mantle cell lymphoma
    9673/3
    2A85.5
  - Burkitt lymphoma
    9687/3
    2A85.6
  - Chronic lymphocytic leukemia / small lymphocytic lymphoma
    9823/3
    2A82.0Z
  - B lymphoblastic leukemia / lymphoma
    9811/3
    C83.5 & C91.0
  - Secondary lymphomatoid granulomatosis
    9766/1 & 9766/3
Cutaneous T cell and NK cell lymphoproliferative disorders and neoplasms
- Reactive T cell rich lymphoid proliferations
- Primary cutaneous T cell disorders
  - Primary cutaneous CD4+ small or medium T cell
    9709/1
    2B0Y & XH3QE7
    
    lymphoproliferative disorder
  - Mycosis fungoides
    9700/3
    2B01
  - Primary cutaneous CD30+ T cell lymphoproliferative disorder:
    9718/1
    2B03.1
    
    lymphomatoid papulosis
  - Primary cutaneous CD30+ T cell lymphoproliferative disorder:
    2B03.0 & XH40C0
    2B03.0 & XH3400
    
    primary cutaneous anaplastic large cell lymphoma
  - Subcutaneous panniculitis-like T cell lymphoma
    9708/3
    2B00
  - Primary cutaneous gamma / delta T cell lymphoma
    9726/3
    2B04 & XH84A5
  - Primary cutaneous acral CD8+ T cell
    9709/3
    2B0Y & XH7S84
    
    lymphoproliferative disorder
  - Primary cutaneous CD8+ aggressive epidermotropic
    9709/3
    2BOY & XH2513
    
    cytotoxic T cell lymphoma
  - Primary cutaneous peripheral T cell lymphoma, NOS
    9702/3
    2B0Z
  - Sézary syndrome
    9701/3
    2B02
- EBV+ lymphoproliferative diseases of childhood
  - Severe mosquito bite allergy
  - Hydroa vacciniforme lymphoproliferative disorder
    9725/1
    2B0Y & XH0AK5
- Secondary cutaneous involvement in T cell and NK cell lymphomas and leukemias
  - Anaplastic large cell lymphoma
    9714/3 & 9715/3
    2A90.B
  - Nodal T follicular helper lymphoma, angioimmunoblastic type
    9705/3
    2A90.9
  - T cell prolymphocytic leukemia
    9834/3
    2A90.0
  - T lymphoblastic leukemia / lymphoma
    9837/3
    2A71 & XH50W
  - Adult T cell leukemia / lymphoma
    9827/3
    2A90.5
  - Extranodal NK / T cell lymphoma
    9719/3
    2A90.6
Other cutaneous lymphoproliferative disorders
- Lymphoproliferative disorders and lymphomas associated
  with immunodeficiency and dysregulation
  - EBV+ mucocutaneous ulcer
    9680/1
    2B0Y & XH3SG2
  - Inborn error of immunity associated lymphoproliferative disorders
    
    4A01.Z

Soft tissue tumors

ICD-O

ICD-11

Adipocytic tumors
- Nevus lipomatosus superficialis
- Lipoma
  8850/0
  2E80.0Z
- Angiolipoma
  8861/0
  2E80.0YZ & XH3C77
- Spindle cell / pleomorphic lipoma
  8857/0
  2E80.0
- Atypical lipomatous tumor
  8850/1
  2F7C & XH0RW4
- Pleomorphic liposarcoma
  8854/3
  2B59.Y & XH25R1
Fibroblastic, myofibroblastic and fibrohistiocytic tumors
- Benign fibroblastic, myofibroblastic and fibrohistiocytic neoplasms
  - Fibroma of tendon sheath
    8813/0
    EE6Y & XH0WB3
  - Calcifying aponeurotic fibroma
    8816/0
    EE6Y & XH8ZE3
  - Sclerotic fibroma
    8810/0
    2F23.Y & XH5JG7
  - Nuchal type fibroma
    8810/0
    EE6Y & H0XH6
  - Gardner fibroma
    8810/0
    EE6Y & XH7GT0
  - Pleomorphic fibroma
    8810/0
    XH1BV2 & 2F23
  - Elastofibroma
    8820/0
    FB51.Y & XH3BQ8
  - Desmoplastic fibroblastoma
    8810/0
    EE6Y & XH2ZF3
  - Fibrous papule
    9160/0
    2F23.Y
  - Fibroblastic connective tissue nevus
    8810/0
    2B53.1
  - Fibro-osseous tumor of digits
    
    FB51.Y
  - Dermatofibroma (fibrous histiocytoma)
    8832/0
    2F23.0
  - Superficial fibromatosis
    8813/1
    FB51.Y & XH75J5
  - Inclusion body fibromatosis
    
    EE6Y
  - Plexiform fibrohistiocytic tumor
    8835/1
    2F7C & XH4GL1
  - Superficial acral fibromyxoma
    8811/0
    EE6Y & XH8173
  - Cutaneous myxoma (superficial angiomyxoma)
    8840/0
    2E84.0 & XH58A9
  - Dermatomyofibroma
    8824/0
    2F23.Y & XH18K3
  - Multinucleate cell angiohistiocytoma
    8810/0
    2F23.Y
  - Plaque-like CD34+ dermal fibroma
    8810/1
    2B53.Y & XH3665
  - Nodular fasciitis
    8828/0
    FB51.2 & XH5LM1
  - EWSR1::SMAD3 rearranged fibroblastic tumor
    
    2B53.Y
- Intermediate fibroblastic, myofibroblastic and fibrohistiocytic neoplasms
  - Dermatofibrosarcoma protuberans
    8832/1
    2B53.Y & XH4QZ8
  - Myxoinflammatory fibroblastic sarcoma
    8811/1
    2B5F.2 & XH2D15
Vascular tumors
- Hemangiomas
  - Cherry hemangioma
    9120/0
    2F25 & XH9Q71
  - Sinusoidal hemangioma
    9120/0
    2F2Y & XH88L5
  - Microvenular hemangioma
    9120/0
    2F2Y & XH9UU3
  - Hobnail hemangioma
    9120/0
    LA90.1Z & XH8PD3
  - Glomeruloid hemangioma
    9120/0
    2F2Y & XH9NB0
  - Papillary hemangioma
    9120/0
    2F2Y
  - Spindle cell hemangioma
    9120/0
    2F2Y & XH6RP8
  - Epithelioid hemangioma
    9125/0
    2F2Y & XH10T4
  - Tufted hemangioma
    9161/0
    2F2Y & XH2EX4
  - Angiokeratoma
    9141/0
    EF20.1
  - Infantile hemangioma
    9131/0
    2E81.2Y & XH3U29
  - Congenital nonprogressive hemangiomas: rapidly involuting
    9131/0
    2E81.2Y & XH5427
    
    congenital hemangioma and noninvoluting congenital hemangioma
  - Lobular capillary hemangioma
    9131/0
    2F26
  - Poikilodermatous plaque-like hemangioma
    9120/0
    2F2Y
  - Acquired elastotic hemangioma
    9120/0
    2F2Y
  - Verrucous venous malformation
    9141/0
    2F2Y & XH23S6
  - Arteriovenous malformation
    9123/0
    LA90.3Y
- Other benign vascular tumors
  - Lymphangioma (superficial lymphatic malformation)
    9170/0
    LA90.12 & XH9MR8
  - Cutaneous epithelioid angiomatous nodule
    9125/0
    2F2Y & XH8SM9
  - Postradiation atypical vascular lesion
    9126/0
    2E81.Y & XH8KN7
- Intermediate vascular neoplasms
  - Pseudomyogenic hemangioendothelioma
    9138/1
    2E81.OZ & XH26F6
  - Epithelioid hemangioendothelioma
    9133/3
    2B5Y & XH9GF8
  - Hobnail hemangioendothelioma
    9135/1 & 9136/1
    2F72.Y & XH4S47
  - Composite hemangioendothelioma
    9136/1
    2F72.Y & XH8D24
  - Kaposi sarcoma
    9140/4
    2B57.Z
- Malignant vascular sarcomas
  - Cutaneous angiosarcoma
    9120/3
    2B56.Y & XH6264
Pericytic and perivascular tumors
- Benign pericytic and perivascular neoplasms
  - Glomus tumor
    8711/0
    2E81.0Y
  - Myopericytoma
    8824/0
    2E84.Y & XH2HE9
  - Myofibroma and myofibromatosis
    8824/0
    2E84.Y & XH0953
  - Angioleiomyoma
    8894/0
    2E86.1 & XH7CL0
Smooth muscle tumors
- Benign smooth muscle neoplasms
  - Smooth muscle hamartoma
    
    LC02
  - Cutaneous leiomyomas
    8890/0
    2F2Y & XH4CY6
  - EBV associated smooth muscle tumor
    8897/1
    2F9C
- Intermediate smooth muscle neoplasms
  - Atypical intradermal smooth muscle neoplasm
    8897/1
    2F9C & XH1EN1
Neural tumors
- Benign neural neoplasms
  - Dermal hyperneury / epithelial sheath neuroma
    9570/0
    2F24 & XH4UE6
  - Solitary circumscribed neuroma
    9570/0
    2F24 & XH90Y8
  - Dermal nerve sheath myxoma
    9562/0
    2F24 & XH3L35
  - Perineurioma
    9571/0
    2F3Y & XH0XF7
  - Neurofibroma
    9540/0 & 9541/0
    2F23 & XH87J5
  - Schwannoma
    9560/0
    2F24 & XH98Z3
  - Granular cell tumor
    9580/0
    2E89.1 & XH09A9
  - Hybrid nerve sheath tumors
    9563/0
    2F24 & XH01G0
- Malignant neural neoplasms
  - Malignant peripheral nerve sheath tumor
    9540/3
    2B5E
Tumors of uncertain differentiation
- Benign neoplasms of uncertain differentiation
  - Cellular neurothekeoma
    9562/0
    2F24 & XH1UZ6
  - Epithelioid fibrous histiocytoma
    8830/0
    2E85.2 & XH15M9
  - Nonneural granular cell tumor
    8990/1
    2E89.1 & XH5LL8
  - PEComa
    8714/0
    2E8Y & XH4CC6
- Intermediate neoplasms of uncertain differentiation
  - Angiomatoid fibrous histiocytoma
    8836/1
    2F7C & XH9362
  - NTRK rearranged spindle cell neoplasm
  - Atypical fibroxanthoma
    8833/0
    2F72.Y & XH1RM7
  - Superficial CD34+ fibroblastic tumor
    8810/1
    2B53.Y
- Malignant neoplasms of uncertain differentiation
  - Pleomorphic dermal sarcoma
    8802/3
    2C35 & XH7XH3
  - Epithelioid sarcoma
    8804/3
    2B5F.2 & XH4F96
  - CRTC1::TRIM11 cutaneous tumor
    9044/3
    2C35
  - Dermal clear cell sarcoma
    9044/3
    2C35 & XH77N6
  - Ewing sarcoma
    9364/3
    2B52.3 & 2B52.Y

Metastases to skin

ICD-O

ICD-11

Metastases to skin

2E08
Cancer of unknown primary site
8010/6

Genetic tumor syndromes associated with skin malignancies

ICD-11

Familial melanoma
BAP1 tumor predisposition syndrome
Xeroderma pigmentosum
LD27.1
Nevoid basal cell carcinoma syndrome (Gorlin syndrome)
LD2D.4
Carney complex
Muir-Torre syndrome
Brooke-Spiegler and related syndromes
2F22

Microscopic (histologic) images

Contributed by Jonathan D. Ho, M.B.B.S., D.Sc.

Keratoacanthoma

Bowen disease (squamous cell carcinoma in situ)

Merkel cell carcinoma

Syringocystadenoma
papilliferum

Eccrine
syringofibroadenoma

Ductule formation in
syringofibroadenoma

Microcystic adnexal carcinoma

Trichilemmoma

Malignant proliferating trichilemmal tumor

Eccrine porocarcinoma

Onychomatricoma

Onychomatricoma
keratinization

Mycosis fungoides

Primary cutaneous anaplastic large cell lymphoma

CD30 positivity in ALCL

Adult maculopapular cutaneous mastocytosis

Angiolipoma

Dermatofibrosarcoma
protuberans

Cutaneous angiosarcoma

Schwannoma

Kaposi sarcoma

HHV8 in Kaposi sarcoma

Additional references

WHO Classification of Tumours Editorial Board: Skin Tumours, 5th Edition, 2022

Board review style question #1

Which of the following statements is true regarding Merkel cell carcinoma?

Characterized by a coarse chromatin pattern
Considered a tumor of neural origin
Has an indolent course
May be associated with polyomavirus infection
Typically expresses CK7

Board review style answer #1

D. May be associated with polyomavirus infection. Merkel cell polyomavirus may be seen in up to 80% of tumors in some populations. Answer A is incorrect because Merkel cell carcinoma is characterized by finely dispersed salt and pepper chromatin. Answer B is incorrect because Merkel cell carcinoma is classified as a cutaneous neuroendocrine tumor. Answer C is incorrect because Merkel cell carcinoma has an aggressive course with metastatic potential. Answer E is incorrect because Merkel cell carcinoma is typically CK20+ and CK7-. Only very rare cases of CK7+ have been described.

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Reference: Skin nonmelanocytic tumor - WHO classification

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