Skin melanocytic tumor
Melanocytic tumors on acral skin and nail apparatus
Acral melanoma
Author: Christopher S. Hale, M.D.
Topic Completed: 1 May 2013
Minor changes: 3 November 2020
Copyright: 2002-2021, PathologyOutlines.com, Inc.
PubMed Search: Acral melanoma (ALM)
Table of Contents
Definition / general | Epidemiology | Sites | Clinical features | Prognostic factors | Case reports | Clinical images | Dermoscopy | Microscopic (histologic) description | Microscopic (histologic) images | Positive stains | Molecular / cytogenetics description | Differential diagnosisCite this page: Hale CS. Acral melanoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticacrallentiginous.html. Accessed September 19th, 2021.
Definition / general
- Acral: relating to or affecting the glabrous (nonhair bearing) or volar skin of the soles, palms and digits as well as the nail apparatus
- Note: all melanomas of acral sites do NOT have histology of acral lentiginous melanoma (Br J Dermatol 2012;166:727)
Epidemiology
- Rare; age adjusted incidence of 1.8 per million person years (Arch Dermatol 2009;145:427)
- More common in blacks and Asians; ~10% of melanomas in whites
- Older age than other variants (66 vs. 52 years), associated with other malignancies; less often associated with sunburn
Sites
- Usually palms and soles, subungual, mucocutaneous oral and nasal cavity or anus
Clinical features
- Often advanced at diagnosis because thickened, hyperkeratotic epidermis overlies and hides primary lesion; often initially misdiagnosed (J Am Acad Dermatol 2003;48:183)
- May evolve slowly over years; mean 1 year to diagnosis in foot / ankle lesions (J Foot Ankle Res 2008;1:11)
- Rarely multiple (Dermatol Surg 2007;33:1)
- Median disease free survival is 10 years (Br J Dermatol 2006;155:561)
- In situ cases show longitudinal pigmented streak in nail plates, black pigmentation on proximal or lateral nail fold, irregular border or variegated pigmentation on sole or thumb (Am J Dermatopathol 2004;26:285)
- Invasive cases show densely pigmented macules with irregular borders; mean 3 mm, usually ulcerated (74%, Cancer Causes Control 2009;20:115)
Prognostic factors
- High mitotic rate, microsatellites (Br J Dermatol 2007;157:311)
- Positive sentinel lymph nodes are dominant factor for recurrence (Am J Surg 2012;204:874)
Case reports
- 42 year old woman with lesion initially treated as plantar wart (Dermatol Online J 2006;12:3)
- 74 year old man with in situ ALM which progressed to invasion (Ann Dermatol 2009;21:185)
Clinical images
Images hosted on other servers:
Plantar surface
Erosive and macerated lesion
In situ 5 years ago (fig. A)
Invasive ALM (fig. A and B)
Dermoscopy
- May have parallel ridge pattern (band-like pigmentation on ridges of skin markings is specific)
Microscopic (histologic) description
- Confluent single cell melanocytic proliferation
- Variable cytologic atpyia of melanocytes
- Prominent acanthosis of epidermis with elongated rete ridges
- Pagetoid spread
- Proliferation of melanocytes downward along eccrine ducts
- Melanocytes may display prominent dendritic proceses
- Invasive component often composed of spindle cells but epithelioid, small cells and pleomorphic cells are occasionally noted
- Intraepidermal lentiginous component is similar to lentigo maligna but intraepidermal melanocytes are bizarre, epidermis is markedly hyperplastic and papillary dermis is widened and inflamed
- Consumption of epidermis present (attenuation of basal / suprabasal layers with rete ridge loss, J Cutan Pathol 2012;39:577)
- Early lesions may show proliferation of solitary melanocytes in crista profunda intermedia, the epidermal rete ridge underlying the ridge of the skin marking (Am J Dermatopathol 2006;28:21)
- Nail lesions show confluent stretches of solitary melanocytes, multinucleation, lichenoid inflammatory reaction and florid pagetoid spread (Am J Surg Pathol 2008;32:835)
Microscopic (histologic) images
Contributed by Angel Fernandez-Flores, M.D., Ph.D.
Acral lentiginous melanoma
Images hosted on other servers:
In situ (fig. B)
Invasion: nest formation by melanoma cells (fig. C and D)
Positive stains
Molecular / cytogenetics description
- 87% have RAS pathway mutations (Exp Dermatol 2013;22:148)
Differential diagnosis
