Skin melanocytic tumor
Melanoma
Desmoplastic melanoma

Editor-in-Chief: Debra L. Zynger, M.D.
Said Albahra, M.D.
Gregory A. Hosler, M.D., Ph.D.

Topic Completed: 21 June 2021

Minor changes: 21 June 2021

Copyright: 2002-2021, PathologyOutlines.com, Inc.

PubMed Search: desmoplastic melanoma "free full text"[sb]

Said Albahra, M.D.
Gregory A. Hosler, M.D., Ph.D.
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Cite this page: Albahra S, Hosler GA. Desmoplastic melanoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticdesmoplasticmelanoma.html. Accessed July 24th, 2021.
Definition / general
  • Rare desmoplastic / fibrosing variant of spindle cell melanoma with > 90% stroma / collagen
Essential features
  • Often amelanotic and mistaken for nonmelanocytic lesion, such as scar
  • Prognosis variable, dependent on presence of conventional melanoma
  • Positive for SOX10 and S100 but often negative for other melanocytic markers
  • Nodular lymphoid aggregates are a useful clue
Terminology
  • Pure form: tumor predominantly / entirely desmoplastic (≥ 90%)
  • Mixed form: significant component of conventional melanoma (> 10%)
ICD coding
  • ICD-O: 8745/3 - desmoplastic melanoma, malignant
  • ICD-10: C43.9 - malignant melanoma of skin, unspecified
Epidemiology
Sites
  • Head and neck region most common
Pathophysiology
Etiology
  • Unclear
  • Mostly arises in a background of severe sun damage
Clinical features
  • Often nonpigmented and misdiagnosed as scar
  • Usually advanced thickness at presentation (Br J Dermatol 2005;152:673)
  • Dermoscopy is difficult due to absence of pigmented network
Diagnosis
  • Diagnosis can be made on biopsy but paucicellular variant is easily misdiagnosed
Prognostic factors
  • 5 year disease free survival: 68% (J Am Acad Dermatol 1995;32:717)
  • Prognosis related to
    • Neurotropism: presence linked to significantly reduced survival
    • Histologic type
      • Pure form biologically behaves as sarcoma with frequent local recurrence and metastasis to lung
      • Mixed form akin to conventional melanoma with metastasis to lymph node
Case reports
Treatment
  • Wide local excision
  • Adjuvant radiotherapy can be considered for pure form with perineural invasion, Breslow thickness > 4 mm or positive surgical margins (Melanoma Res 2016;26:35)
Clinical images

Images hosted on other servers:
Forearm lesion

Forearm lesion

Dermoscopy

Dermoscopy

Mandible lesion

Mandible leasion

Gross description
  • Pigmented or scar-like skin surface with ill defined induration (JAMA Dermatol 2013;149:413)
  • Cross sections with white, poorly demarcated tumor
Microscopic (histologic) description
  • Poorly circumscribed with deep infiltration
  • Elongated spindle cell surrounded by collagen bundles (Hum Pathol 1983;14:1072)
    • Can resemble fibroblasts
    • Scattered cells show hyperchromasia and bizarre nuclei
    • Multinucleated cells often present
  • Stromal component varies in different tumors (Mod Pathol 2014;27:524)
    • Some tumors with scattered spindle cells and abundant collagen
    • Others with high cellularity and little stroma (best classified as spindle cell melanoma)
  • Small foci of lymphoid aggregates is a useful clue to the diagnosis on scanning
  • May be pure or combined with classic melanoma
  • Desmoplastic neurotropic melanoma considered a variant (33% of all cases of desmoplastic melanoma) (Am J Dermatopathol 2008;30:207)
Microscopic (histologic) images

Contributed by Gregory A. Hosler, M.D., Ph.D.
Pure type

Pure type

Atypia, pure type

Atypia, pure type

Mixed type

Mixed type

Lymphoid aggregates

Lymphoid aggregates

Neurotropism

Neurotropism


Mitosis

Mitosis

S100

S100

SOX10

SOX10

Spindle cell melanoma

Spindle cell melanoma

Virtual slides

Images hosted on other servers:
Desmoplastic melanoma

Desmoplastic melanoma

Cytology description
  • Clean background; aggregates of pleomorphic spindle cells mixed with fibrous stroma and single cells
  • Fine, wispy and delicate cytoplasm at nuclear poles; elongated and plump nuclei with irregular contours; deep grooves and folds and dark coarse chromatin with variably prominent nucleoli (Cytojournal 2007;4:18)
  • Less cellular with fewer intranuclear cytoplasmic inclusions and mitoses relative to conventional melanoma (Am J Clin Pathol 2008;130:715)
Positive stains
Negative stains
Electron microscopy description
  • Shows only modest evidence of melanocytic origin
    • Stage II melanosomes considered the hallmark of melanoma and melanin synthesis
    • Some cases with nonmembrane bound melanin granules and premelanosomes (Hum Pathol 1983;14:1072)
  • Cells have abundant rough endoplasmic reticulum and sometimes intracytoplasmic collagen and macular desmosomes
Molecular / cytogenetics description
  • NF1 loss of function mutations common
  • Numerous point mutations
  • In contrast, other melanomas have genetic copy number alternations
  • NFKBIE (NFκB inhibitor, epsilon; 6p21.1) promoter mutations appear to play a role in development (Nat Genet 2015;47:1194)
  • BRAF mutations unusual
  • Sensitivity of FISH assay ~ 50% (using a 4 probe FISH assay targeting RREB1, MYB, CEP6 and CCND1 (J Cutan Pathol 2011;38:329)
  • Sensitivity of both single nucleotide polymorphism array and gene expression profiling 50 - 80% (Hum Pathol 2017;70:113)
Videos

Desmoplastic melanoma: 5 minute pathology pearls

Sample pathology report
  • Skin, scalp, shave biopsy:
    • Desmoplastic melanoma (pure type), level IV, 1.3 mm tumor thickness, nonulcerated
Differential diagnosis
Board review style question #1

A 65 year old man presents with a lesion on the scalp. Biopsy shows a spindle cell neoplasm centered in the dermis. The tumor cells express S100 and are negative for CD34, desmin, CD10 and cytokeratins. Regarding this entity, which of the following statements is true?

  1. Frequently metastasizes to lymph node
  2. MART1 is always positive
  3. Nodular lymphoid aggregates are a useful clue to the diagnosis
  4. Often clinically suspected at the time of biopsy
  5. Site of predilection is the trunk
Board review style answer #1
C. Nodular lymphoid aggregates are a useful clue to the diagnosis. This is a desmoplastic melanoma.

Comment Here

Reference: Desmoplastic melanoma
Board review style question #2

Which of the following is most commonly expressed in desmoplastic melanoma?

  1. CD34
  2. HMB45
  3. MART1
  4. MITF
  5. SOX10
Board review style answer #2
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