Skin - Nonmelanocytic tumors
Benign (nonmelanotic) epidermal tumors or tumor-like lesions
Cutaneous melanoacanthoma

Author: Hillary Elwood, M.D. (see Authors page)

Revised: 13 January 2016, last major update January 2016

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Cutaneous melanoacanthoma [title]
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

Images hosted on Other servers:

Missing Image Missing Image Missing Image

Various images

Missing Image Missing Image

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
Micro 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
Micro Images

Images hosted on Other servers:

Missing Image

Hyperkeratosis and papillomatosis

Missing Image

Hyperkeratosis and acanthosis

Missing Image

Acanthotic epidermis

Missing Image

Basaloid cells

Missing Image

S100, Fontana-Masson, HMB45

Missing Image

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'