Skin melanocytic tumor

Melanoma

Melanomas with unusual features (balloon cell, verrucous, signet ring cell, small cell, etc.)



Last author update: 29 February 2024
Last staff update: 29 February 2024

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PubMed Search: Melanomas with unusual features

Marialessandra Capuzzolo, M.D.
Gerardo Cazzato, M.D., Ph.D.
Page views in 2024 to date: 995
Cite this page: Capuzzolo M, Cazzato G. Melanomas with unusual features (balloon cell, verrucous, signet ring cell, small cell, etc.). PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumormelanocyticmelanomaunusual.html. Accessed April 14th, 2024.
Definition / general
Essential features
  • Melanoma can present with rare and unusual histomorphological forms (variants) that account for < 1% of cases
  • Morphological peculiarities do not always translate to a worsening prognosis
  • Appropriate histological description and immunohistochemical markers allow us to reach a precise and detailed diagnosis of unusual forms of melanoma
  • It is essential to consider the differential diagnoses of particular forms of melanoma
Terminology
ICD coding
  • ICD-10: C43.9 - malignant melanoma of skin, unspecified
  • ICD-11
    • 2C30.Y - other specified melanoma of skin
    • 2C30.Z - melanoma of skin, unspecified
Epidemiology
Sites
  • Balloon cell: choroid (14%) and other locations
  • Melanoma with rhabdomyosarcomatous differentiation: metastatic setting (lymph nodes, soft tissue, liver) more common than primary cutaneous (scalp, trunk, extremities) (Int J Clin Exp Pathol 2014;7:840)
  • Verrucous: more common in face and limbs
  • Signet ring cell: metastatic setting more common than primitive
  • Small cell, 2 forms
    1. Develops in large congenital nevus
    2. Develops in children, de novo, on the scalp
  • Myxoid: metastatic more common than primary mucocutaneous (skin, nasal sinuses, conjunctiva, gastrointestinal system)
  • Osteogenic: more common on acral skin and nail bed; occasional mucosal involvement
Clinical features
Diagnosis
  • Excisional biopsy
  • Incisional biopsy
  • Shave or punch biopsy with adequate breadth and depth
Case reports
Microscopic (histologic) description
  • Balloon cell
    • Melanocytes with abundant and finely vacuolated cytoplasm, scattered dusty melanin granules (Dermatopathology (Basel) 2022;9:100)
    • Nuclei are pleomorphic with occasional prominent nucleoli
    • Mitoses are rare, something found only in hot areas
    • Frequent involvement of the dermis and subcutis
  • Rhabdoid
    • Rhabdoid cells have plasmacytoid appearance, round to oval contour and large amounts of cytoplasm with refractive, deeply eosinophilic material (Int J Clin Exp Pathol 2014;7:840)
    • Nuclei are crescent or round shaped, disposed polar to the cytoplasm against the cellular membrane
    • Hyperchromatism, pleomorphism, high mitotic rate and single cell necrosis are frequent
  • Verrucous
    • Striking epidermal and adnexal hyperplasia with thickened epidermis, dyskeratotic cells, squamous eddies and keratotic cysts (Cureus 2022;14:e29098)
    • Strikingly atypical proliferation of melanocytes at the junction and in the dermis
    • Rare pagetoid spread
  • Signet ring
    • Large cells containing a big roundish cytoplasmic vacuole (Am J Dermatopathol 2014;36:985)
    • Nuclei seem to be pushed against the cell membrane, with a crescent shaped silhouette
  • Small cell
    • 2 variants: small cells, so called non-Merkel tumor-like cell variant and large cells, Merkel cell tumor-like variant (Dermatopathology (Basel) 2019;6:231)
    • Small or barely visible cytoplasm with hyperchromatic nucleus with coarse chromatin
    • Cells are atypical and mitoses are easily found
    • No maturation as the lesion goes deeper
    • Monotonous cells
    • Pigment is usually rare and focal
  • Myxoid
    • Dendritic or stellate melanocytes scattered in abundant mucinous material
    • Large nuclei and irregularly clumped nuclear chromatin (J Am Acad Dermatol 2002;46:264)
    • Rare mitoses in myxoid background
    • Scarce melanin
  • Osteogenic (osseocartilaginous differentiation)
  • Dedifferentiated / undifferentiated
    • Pleomorphic, atypical cells, with numerous mitotic figures; nuclei with thinned chromatin and numerous central and peripheral nucleoli (Am J Surg Pathol 2021;45:240)
Microscopic (histologic) images

Contributed by Gerardo Cazzato, M.D., Ph.D.
Melanocytes with clear / balloon cytoplasm

Melanocytes with clear / balloon cytoplasm

Balloon cell with atypia

Balloon cell with atypia

Rhabdoid melanocytes within necrosis

Rhabdoid melanocytes within necrosis


Rhabdoid melanocytes with mitoses Rhabdoid melanocytes with mitoses

Rhabdoid melanocytes with mitoses

Striking atypical melanocytic proliferation

Striking atypical melanocytic proliferation

Melanoma with pseudo-epitheliomatous hyperplasia

Melanoma with pseudo-epitheliomatous hyperplasia



Images hosted on other servers:
Signet ring cell melanoma

Signet ring cell melanoma

Small cell melanoma

Small cell melanoma

Myxoid melanoma

Myxoid melanoma

Positive stains
Negative stains
Molecular / cytogenetics description
  • Dedifferentiated / undifferentiated: detection of a melanoma compatible gene mutation, such as BRAF or NRAS, aids in diagnosis (Am J Surg Pathol 2021;45:240)
Videos

Rhabdoid melanoma

Small cell melanoma

Sample pathology report
  • Limb skin, excisional biopsy:
    • Melanoma with rhabdoid cell features (see comment)
    • Comment: Sections of skin and subcutis including a proliferation of cells with a plasmacytoid appearance, characterized by round / oval outlines and large amounts of cytoplasm containing eosinophilic material with a glassy hyaline but sometimes filamentous appearance. The cell nuclei (hyperchromatic, pleomorphic) are crescent shaped or round and arranged polar to the cytoplasm against the cellular membrane.
Differential diagnosis
Board review style question #1

A 61 year old man with a history of melanoma of the right preauricular region presents with right lateral cervical swelling. Which of the following statements is true regarding this entity?

  1. Clinical features are pathognomonic
  2. S100 and HMB45 are almost always positive
  3. S100 is usually negative
  4. This lesion is usually primary cutaneous
Board review style answer #1
B. S100 and HMB45 are almost always positive. Despite the morphological peculiarities of rhabdoid melanoma, immunohistochemical investigations for neuroectodermal markers, such as S100 protein and HMB45, are almost always invariably positive and help the pathologist in the correct differential diagnosis with other entities of striated muscle lineage. Rhabdoid melanoma can present with widespread and strong positivity for vimentin and sometimes for desmin, while usually MelanA is negative. Answer A is incorrect because rhabdoid melanoma doesn't have any clinical pathognomonic features. Answer C is incorrect because S100 is usually positive, not negative. Answer D is incorrect because the metastatic setting is more common than primary cutaneous setting in case of rhabdoid melanoma.

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Reference: Melanomas with unusual features
Board review style question #2
What are the characteristics that allow a differential diagnosis between balloon cell melanoma and balloon cell nevus?

  1. Melanin
  2. Mitoses, large nuclei, distinct and large nucleoli, architecture of the neoplasm and intraepidermal pagetoid scatter of balloon cells
  3. Percentage of balloon cell component
  4. Positivity for MelanA
Board review style answer #2
B. Mitoses, large nuclei, distinct and large nucleoli, architecture of the neoplasm and intraepidermal pagetoid scatter of balloon cells. It is important to remember that the parameters used in the differential diagnosis of common forms of melanoma are the same as with unusual and rare forms of melanoma; therefore, in differentiating a balloon cell melanoma from a balloon cell nevus, it is essential to rely on the criteria we know. Answer D is incorrect because positivity for MelanA is not useful for a differential diagnosis. Answer A is incorrect because presence of melanin is not a criterion. Answer C is incorrect because the percentage of melanocytes with balloon cell appearance is useful for the diagnosis of a balloon cell lesion but not in distinguishing a nevus from a melanoma.

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Reference: Melanomas with unusual features
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