Skin nonmelanocytic tumor
Benign (nonmelanotic) epidermal tumors or tumor-like lesions
Melanoacanthoma


Topic Completed: 1 January 2016

Minor changes: 24 September 2020

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PubMed Search: Cutaneous melanoacanthoma [title]

Hillary Rose Elwood, M.D.
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Cite this page: Elwood H. Melanoacanthoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/skintumornonmelanocyticmelanoacanthoma.html. Accessed September 30th, 2020.
Definition / general
  • Benign pigmented lesion composed of melanocytes and keratinocytes
  • Best regarded as a variant of seborrheic keratosis
  • Oral melanoacanthoma or melanoacanthosis is clinically distinct from cutaneous melanoacanthoma
    • Oral melanoacanthoma is likely reactive, possibly a form of postinflammatory hypermelanosis, and not a tumor-like proliferation
    • It is not discussed as part of this topic
Case reports
Clinical images

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Various images

Ulcerated plaque Ulcerated plaque

Ulcerated plaque

Gross description
  • Pigmented plaque, papule or nodule with dull surface
  • Usually solitary and slow growing lesion on head and neck or trunk of older individuals
  • Can clinically mimic a seborrheic keratosis or melanoma
  • Large variants have been described, up to 3 cm or more
Microscopic (histologic) description
  • Resembles a seborrheic keratosis with acanthotic or slightly verrucous epidermis containing small cuboidal keratinocytes and numerous dendritic melanocytes
  • The dendritic melanocytes are heavily pigmented with abundant melanin granules
  • Most melanin pigment is contained within the dendritic melanocytes with little transfer to adjacent keratinocytes
  • Dendritic melanocytes express usual markers of melanocytic differentiation (i.e. S100, HMB45, MelanA)
  • Often has overlying compact eosinophilic parakeratosis even when not irritated
  • No significant cytologic atypia present
Microscopic (histologic) images

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Hyperkeratosis and papillomatosis

Hyperkeratosis and papillomatosis

Hyperkeratosis and acanthosis

Hyperkeratosis and acanthosis

Basaloid cells

Basaloid cells

Masson-Fontana

Masson-Fontana

Electron microscopy description
  • Composed of benign keratinocytes and dendritic melanocytes
  • Incomplete transfer of pigment from melanocytes to keratinocytes, normal population of Langerhan cells (J Cutan Pathol 1978;5:127)
Differential diagnosis
  • Melanoma:
    • While the dendritic melanocytes in melanoacanthoma might be confused for intraepidermal spread of melanocytes, the melanocytes lack atypia and are part of a background keratinocytic proliferation
  • Pigmented hidroacanthoma / poroma:
    • Contains discrete smooth bordered intraepidermal cellular aggregates with ductal differentiation
    • Melanin pigmentation not restricted to pigmented melanocytes
  • Pigmented squamous cell carcinoma in situ:
    • Full thickness intraepidermal keratinocytic atypia with mitoses and pigment in keratinocytes
  • Seborrheic keratosis:
    • Melanoacanthoma is a variant of seborrheic keratosis so the distinction is not critical
    • Some might sign out melanoacanthoma as seborrheic keratosis, or might use melanoacanthoma with the additional descriptor of 'benign variant of seborrheic keratosis with prominent dendritic melanocytes'
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