Skin nonmelanocytic tumor

General

WHO classification



Last author update: 20 September 2023
Last staff update: 26 February 2024

Copyright: 2023-2024, PathologyOutlines.com, Inc.

PubMed Search: Skin nonmelanocytic tumor WHO

Chico J. Collie, M.B.B.S.
Jonathan D. Ho, M.B.B.S., D.Sc.
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Cite this page: Collie CJ, Ho JD. WHO classification. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skinnonmelanocyticWHO.html. Accessed May 19th, 2024.
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
    • 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)










    Metastases to skin
    ICD-O
    ICD-11


    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

Keratoacanthoma

Bowen disease (squamous cell carcinoma in situ)

Bowen disease (squamous cell carcinoma in situ)

Merkel cell carcinoma

Merkel cell carcinoma

Syringocystadenoma papilliferum

Syringocystadenoma
papilliferum

Eccrine syringofibroadenoma

Eccrine
syringofibroadenoma

Ductule formation in syringofibroadenoma

Ductule formation in
syringofibroadenoma


Microcystic adnexal carcinoma

Microcystic adnexal carcinoma

Trichilemmoma

Trichilemmoma

Malignant proliferating trichilemmal tumor

Malignant proliferating trichilemmal tumor

Eccrine porocarcinoma

Eccrine porocarcinoma

Eccrine porocarcinoma

Eccrine porocarcinoma

Eccrine porocarcinoma

Eccrine porocarcinoma


Onychomatricoma

Onychomatricoma

Onychomatricoma keratinization

Onychomatricoma
keratinization

Mycosis fungoides

Mycosis fungoides

Primary cutaneous anaplastic large cell lymphoma

Primary cutaneous anaplastic large cell lymphoma

CD30 positivity in ALCL

CD30 positivity in ALCL

Adult maculopapular cutaneous mastocytosis

Adult maculopapular cutaneous mastocytosis


Angiolipoma

Angiolipoma

Dermatofibrosarcoma protuberans

Dermatofibrosarcoma
protuberans

Cutaneous angiosarcoma

Cutaneous angiosarcoma

Schwannoma

Schwannoma

Kaposi sarcoma

Kaposi sarcoma

HHV8 in Kaposi sarcoma

HHV8 in Kaposi sarcoma

Board review style question #1

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

  1. Characterized by a coarse chromatin pattern
  2. Considered a tumor of neural origin
  3. Has an indolent course
  4. May be associated with polyomavirus infection
  5. 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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