Skin nonmelanocytic tumor

Adnexal tumors

Sweat gland derived (apocrine & eccrine glands)

Microcystic adnexal carcinoma

Last author update: 12 March 2024
Last staff update: 12 March 2024

Copyright: 2002-2024,, Inc.

PubMed Search: Microcystic adnexal carcinoma

Christopher Cullison, M.D.
Bethany R. Rohr, M.D.
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Page views in 2024 to date: 5,960
Cite this page: Cullison C, Rohr BR. Microcystic adnexal carcinoma. website. Accessed May 19th, 2024.
Definition / general
  • Microcystic adnexal carcinoma is a rare malignant adnexal tumor with sweat duct and follicular differentiation
Essential features
  • Malignant adnexal carcinoma with sweat duct and follicular differentiation
  • Most commonly occurs on the face of elderly White patients
  • Histopathology shows deep tumor extension with perineural invasion and may show the presence of lymphoid aggregates
  • Tumors may be locally aggressive and Mohs micrographic surgery is the mainstay of treatment
  • Sclerosing sweat duct carcinoma
  • Malignant syringoma
  • Sweat gland carcinoma with syringomatous features
  • Locally aggressive adnexal carcinoma
  • Reference: Mod Pathol 2008;21:178
ICD coding
  • ICD-10: C44.9 - other and unspecified malignant neoplasm of skin, unspecified
  • ICD-11
    • 2C33 - adnexal carcinoma of the skin
    • XH17P2 - microcystic adnexal carcinoma
  • Mutations
    • No signature mutation to date
    • TP53 is the most common mutation (22%)
    • JAK1 (17%)
    • Other oncogenes (JAK2, MAF, MAFB, JUN, FGFR1)
    • Individual cases may harbor ultraviolet pattern of mutations
  • References: Mod Pathol 2020;33:1092, JAMA Dermatol 2019;155:1059
Clinical features
  • Firm, yellow or flesh colored papule, plaque or nodule
  • Mean size at diagnosis: 2.8 cm
  • Rarely metastasizes
  • Reference: JAMA Dermatol 2019;155:1059
Prognostic factors
Case reports
Clinical images

Images hosted on other servers:
White, irregular papule

White, irregular papule

Multiple yellow papulonodules

Multiple yellow papulonodules

Pink and yellow plaque

Pink and yellow plaque

Microscopic (histologic) description
  • Features of both eccrine and follicular differentiation
  • Poorly circumscribed and deeply infiltrating
  • Extension into the subcutaneous adipose tissue and skeletal muscle
  • Superficial pseudohorn cysts containing lamellar keratin
  • Small aggregates of epithelioid cells with curved and angulated shapes, sometimes referred to as having a tadpole-like morphology
  • Deeper components typically have smaller tumor aggregates and can be a single cell layer thick
  • Some islands of tumor cells will show ductal differentiation with luminal centers lined by a pink cuticle
  • Dense fibrous stroma consisting of thick collagen bundles that surround the tumor aggregates
  • Mild cytologic atypia with often bland appearing cells characterized by monomorphic nuclei and scant cytoplasm
  • Lymphoid aggregates adjacent to or in association with tumor
  • Incidental calcifications can be present
  • Mitotic figures are often absent
  • Perineural invasion is a common feature
  • References: Mod Pathol 2008;21:178, Mod Pathol 2006;19:S93
Microscopic (histologic) images

Contributed by Christopher Cullison, M.D. and Bethany R. Rohr, M.D.
Jagged Tumor Islands

Jagged tumor islands

Lymphoid Aggregate

Lymphoid aggregate

Follicular and Ductal Differentiation

Follicular and ductal differentiation

Skeletal muscle invasion

Skeletal muscle invasion

Incidental Calcification

Incidental calcification

Perineural Invasion

Perineural invasion

Virtual slides

Images hosted on other servers:
Deeply invasive tumor islands

Deeply invasive tumor islands

Positive stains

Microcystic adnexal carcinoma by Dr. Jerad Gardner

Differential diagnosis
  • Skin, left cheek, punch biopsy:
    • Microcystic adnexal carcinoma (see comment)
    • Comment: The sections reveal a deeply infiltrating carcinoma with ductal and follicular differentiation. There are surrounding lymphoid aggregates and focal perineural invasion.
Differential diagnosis
Board review style question #1

Which immunohistochemical stain is likely to be positive in the tumor shown above?

  1. AR
  2. CK19
  3. CK20
  4. S100
Board review style answer #1
B. CK19. CK19 has a cytoplasmic staining pattern for eccrine glands and stains positive in 70 - 100% of microcystic adnexal carcinomas. Answer A is incorrect because androgen receptor does not stain positive in microcystic adnexal carcinoma; rather, it typically stains sebaceous glands and apocrine glands. Answer C is incorrect because CK20 is a stain for Merkel cells that is typically lost in microcystic adnexal carcinoma. Answer D is incorrect because S100 is not expressed in microcystic adnexal carcinomas.

Comment Here

Reference: Microcystic adnexal carcinoma
Board review style question #2
Microcystic adnexal carcinoma is most likely to have which of the following findings at diagnosis?

  1. Angiolymphatic invasion
  2. Distant organ metastasis
  3. Lymph node metastasis
  4. Perineural invasion
Board review style answer #2
D. Perineural invasion. Perineural involvement is a common feature in microcystic adnexal carcinomas. Answers A - C are incorrect because metastasis of microcystic adnexal carcinoma is exceedingly uncommon and is not reported to have angioinvasion on pathology.

Comment Here

Reference: Microcystic adnexal carcinoma
Board review style question #3
Which of the following features can differentiate microcystic adnexal carcinoma from syringoma and desmoplastic trichoepithelioma?

  1. Depth of invasion
  2. Presence of ductal differentiation
  3. Presence of follicular differentiation
  4. Sclerotic stroma
Board review style answer #3
A. Depth of invasion. Microcystic adnexal carcinoma typically has a depth of invasion to at least the deep reticular dermis and may invade into subcutaneous structures, including adipose tissue, skeletal muscle or bone. Answer B is incorrect because syringoma will also have presence of ductal differentiation. Answer C is incorrect because desmoplastic trichoepithelioma will also have presence of follicular differentiation. Answer D is incorrect because both syringoma and desmoplastic trichoepithelioma can have a sclerotic stroma.

Comment Here

Reference: Microcystic adnexal carcinoma
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