Skin melanocytic tumor
Melanoma in situ

Author: Christopher Hale, M.D.

Revised: 14 September 2018, last major update April 2013

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Melanoma in situ "loattrfree full text"[sb]

Cite this page: Hale, C.S. Melanoma in situ. website. Accessed October 22nd, 2018.
Definition / general
  • Malignant melanocytes in epidermis, without dermal invasion
  • Variants include lentigo maligna, superficial spreading and acral melanoma
Clinical features
  • Cases in sun damaged skin may resemble benign lichenoid keratosis (Hum Pathol 2003;34:706)
  • Characterized by pagetoid spread, confluence and nesting of atypical melanocytes
  • May be associated with invasive malignant melanoma (Hum Pathol 2000;31:705)
  • Large pigmented lesions, irregular margins and irregular pigmentation
  • Hutchinson sign: periungual extension of brownish black pigmentation from longitudinal melanonychia (pigmented stripe within length of nail bed) onto the proximal and lateral nailfolds
Case reports
Clinical images

Images hosted on other servers:

Various images

Figs 2 - 3: acral lesion with parallel ridge pattern (B)

Before and after Imiquimod cream (A, B)

Fig 1 and 3: various images

Microscopic (histologic) description
  • Atypical melanocytes in epidermis with no dermal invasion
  • Usually epidermal effacement (absences of rete ridges in some foci, J Drugs Dermatol 2007;6:708)
  • Predominance of individual unit melanocytes over nests
  • Confluent growth of melanocytes along dermoepidermal junction
  • Pagetoid spread
  • Involvement of adnexal structures
Microscopic (histologic) images

Images hosted on other servers:

Hyperkeratotic keratosis with coexisting melanoma in situ and MITF staining

Frozen section from Mohs procedure (fig 4)

Limited pagetoid spread in nail (fig 2)


Melanoma in situ

Differential diagnosis