Skin nonmelanocytic tumor

Adnexal tumors

Sweat gland derived (apocrine & eccrine glands)

Poroma


Resident / Fellow Advisory Board: Farres Obeidin, M.D.
Aayushma Regmi, M.B.B.S.
Jodi Speiser, M.D.

Topic Completed: 23 December 2021

Minor changes: 12 January 2022

Copyright: 2002-2022, PathologyOutlines.com, Inc.

PubMed Search: Poroma[TI] "last 5 years"[DP]

Aayushma Regmi, M.B.B.S.
Jodi Speiser, M.D.
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Cite this page: Regmi A, Speiser J. Poroma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticeccrineporoma.html. Accessed January 23rd, 2022.
Definition / general
  • Benign glandular adnexal tumor that usually originates from cells of the outer layer of the acrosyringium and terminal eccrine duct
  • Has both eccrine and apocrine origin (AMA Arch Derm 1956;74:511)
  • Malignant counterpart is referred to as porocarcinoma
Essential features
  • Single, slow growing, asymptomatic, well circumscribed, smooth, skin colored to red, slightly scaly papule or nodule
  • Most commonly on palms and sole or sides of the foot
  • Well circumscribed broad anastomosing bands of poroma cells with sharp demarcation from adjacent keratinocytes
  • Excellent prognosis with simple excision
Terminology
  • Eccrine poroma / hidroacanthoma simplex / dermal duct tumor, apocrine poroma
ICD coding
  • ICD-10: D23.9 - other benign neoplasm of skin, unspecified
Epidemiology
Sites
Pathophysiology
  • Falls under the broad category of poroid neoplasms or acrospiromas
  • Poroid neoplasms include the eccrine poroma, apocrine poroma, hidroacanthoma simplex and dermal duct tumor (Clin Exp Dermatol 2014;39:119)
    • Eccrine poroma: derived from cells of the outer layer of the acrosyringium and the upper dermal eccrine duct, both epidermal and dermal (AMA Arch Derm 1956;74:511)
    • Apocrine poroma: reflects the common embryological ancestry of the 3 units (the folliculosebaceous apocrine unit) (Pathologe 2014;35:456)
Etiology
Clinical features
Diagnosis
  • Clinical appearance confirmed by characteristic histologic findings
Prognostic factors
Case reports
Treatment
Clinical images

Contributed by Aayushma Regmi, M.B.B.S. and Jodi Speiser, M.D.

Pink, scaly nodule

Erythematous nodule

Pedunculated and pigmented nodule

Gross description
Microscopic (histologic) description
  • Eccrine poroma:
    • Well circumscribed
    • Replaces the epidermis and extends into the dermis in broad anastomosing bands
    • Poroma cells are monomorphic, small, cuboidal with basophilic round nuclei, inconspicuous nucleoli and compact eosinophilic cytoplasm
    • Sharp demarcation present between the normal keratinocytes and poroma cells
    • Devoid of peripheral palisading
    • Ductal lumina with single row of luminal cells covered by eosinophilic lining or cystic spaces devoid of any formal lining
    • Cells are united by conspicuous intercellular bridges and supported by a delicate fibrovascular stroma (J Dermatol 1980;7:263)
    • Poroma cells usually contain glycogen (Int J Dermatol 2014;53:1053)
    • Occasionally, pigmented variants with associated dendritic melanocytes and tumor cell melanin deposition (J Dermatol 2010;37:542, J Eur Acad Dermatol Venereol 2008;22:303)
    • Dystrophic calcification and transepidermal elimination of tumor nests are exceptional findings (J Dermatol Case Rep 2009;3:38, J Dermatol 1997;24:539)
  • Apocrine poroma:
    • Shows sebaceous differentiation with the occasional presence of follicular differentiation and foci of apocrine-like features (J Cutan Pathol 2001;28:101)
    • Anastomosing trabeculae, displaying multiple points of origin from the epidermis and located largely in the papillary and upper reticular dermis
    • Cells are small and uniform with scanty cytoplasm and round to oval nuclei united by inconspicuous intercellular bridges
    • Foci of ductal differentiation with a well developed eosinophilic cuticle
    • Follicular differentiation in the form of epithelial lobules (Am J Dermatopathol 1999;21:31)
    • Sebaceous cells, singly and in clusters with bubbly cytoplasm and crenated nuclei is an infrequent feature (Am J Dermatopathol 1996;18:1)
  • Eccrine porocarcinoma:
    • May remain completely intraepidermal (in situ porocarcinoma) but is more often associated with an invasive dermal component
    • Poroma cells, with typical ductal lumina, associated with cytological features of malignancy, including nuclear and cytoplasmic pleomorphism, nuclear hyperchromatism and mitotic activity (Am J Surg Pathol 2001;25:710)
    • Prone to have local recurrence (17%) and is occasionally associated with nodal metastases (19%); however, systemic spread is rare (11%) (Am J Surg Pathol 2001;25:710)
Microscopic (histologic) images

Contributed by Aayushma Regmi, M.B.B.S. and Jodi Speiser, M.D.

Tumor with epidermal connection

Tumor with epidermal connection

Pedunculated nodule


Pigmented poroma

Poroma cells and adjacent keratinocytes

Poroma cells with duct

Hyalinized stroma and blood vessels


Poroma cells

EMA

CK7

CEA

BerEp4

Virtual slides

Images hosted on other servers:

Poroma cells with epidermal connection

Positive stains
Negative stains
Electron microscopy description
  • Cells have numerous connecting desmosomes, cytoplasmic tonofilaments, glycogen granules and intracytoplasmic lumina (J Dermatol 1980;7:263)
Molecular / cytogenetics description
Sample pathology report
  • Skin, left palm, excision:
    • Eccrine poroma, extending to the deep margin
Differential diagnosis
  • Hidroacanthoma simplex:
    • Entirely intraepidermal
    • Discrete circumscribed populations of poroma cells within an irregularly acanthotic epidermis
  • Dermal duct tumor:
    • Entirely intradermal, the epidermis is unaffected
    • Large lobules of uniform poroma cells in the mid and lower dermis
  • Basal cell carcinoma:
    • Nodules, nests or infiltrative cords with proliferation of small basaloid cells and peripheral palisading
    • Stromal retraction artifact between tumor cells and mucinous stroma
    • AE1 / AE3, BerEP4 positive
  • Squamous cell carcinoma (SCC):
    • Lacks evidence of ductal differentiation
    • Squamous differentiation abundant, eosinophilic cytoplasm with keratin pearls, intercellular bridges and keratinization
    • Greater cytologic atypia, dyskeratotic cells
  • Irritated / clonal seborrheic keratosis (SK):
    • Shows follicular differentiation with keratinizing pseudohorn cysts, no ductal differentiation
    • Cells are typically larger than in poroma
  • Hidradenoma:
    • Nests and nodules of epithelial cells lacking epidermal connection
    • Shows both solid and cystic components
    • More commonly shows clear cell features
  • Eccrine syringofibroadenoma:
    • Benign eccrine proliferation
    • Thin anastomosing reticulated cords and strands of basaloid monomorphous cuboidal cells extending from the basal layer of epidermis into dermis
    • Loose fibrovascular stroma
Board review style question #1
Which of the following vascular patterns is observed in the dermatoscopic evaluation of eccrine poroma?

  1. Glomerular
  2. Hairpin
  3. Mosaic
  4. Hairpin and glomerular
  5. Hairpin and mosaic
Board review style answer #1
D. Hairpin and glomerular. The vascular patterns commonly seen in eccrine poroma are the polymorphic, glomerular, linear irregular, leaf and flower-like and looped or hairpin variants. The leaf and flower-like pattern appears to be relatively unique to the poroma. Mosaic pattern is not observed in eccrine poroma (Clin Case Rep 2021;9:1601).

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Reference: Poroma
Board review style question #2

Which of the following is true about eccrine poroma?

  1. Most commonly occurs on central part of the body: frontal scalp, anterior chest and around umbilicus
  2. No distinct demarcation between the poroma cells and adjacent keratinocytes
  3. Presence of monomorphic, basaloid cells with peripheral palisading
  4. Presence of sheets and trabeculae of monomorphic, round basophilic cells containing scattered duct-like structures
Board review style answer #2
D. Presence of sheets and trabeculae of monomorphic, round basophilic cells containing scattered duct-like structures

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Reference: Poroma
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