Malignant melanoma

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Malignant melanoma, also melanoma, is an aggressive type of skin cancer that can be diagnostically challenging for pathologists.

It fits into the larger category of melanocytic lesions which includes many benign entities, a number of which can be difficult to distinguish from melanoma.

General

  • Known as the great mimicker in pathology; it may look like many things.

Pathologic predictors for a poor prognosis:

  • Tumour thickness (Brewslow thickness) > 1 mm.
  • Mitotic rate >1/mm^2.
  • Ulceration.
  • Regression - >75% of tumour.
  • Tumour infiltrating lymphocytes.
  • Microsatellitosis - nest of tumour cells > 0.05 mm size, separated from primary tumour >=0.3 mm and <= 2 cm.
  • In transist metastasis.
  • Lymphovascular invasion.
  • Perineural invasion.

Clinical

  • ABCD = asymmetric, borders (irregular), colour (black), diameter (large).

Serologic predictors of a poor prognosis:

  • Lactate dehydrogenase (LDH) > 200-225 U/L.
  • Alumin < 35 g/L.

Microscopic

Metatstatic/non-skin

Features (non-skin):

  • Classic appearance of melanoma:
    • Loosely cohesive; mix of small nests of cells, single cells.
      • Nests often have clefting with surrounding tissue.
    • Mix of spindle cells and epithelioid cells:
      • +/-Occasional large binucleated cells.
      • Cytoplasm with brown pigment (melanin).
      • Prominent (large) red nucleoli (like in serous carcinoma of the ovary).
      • Marked nuclear pleomorphism - variation in cell size, shape & staining (like in serous carcinoma of the ovary).
      • Nuclear pseudoinclusions (like in papillary thyroid carcinoma).

Notes:

  • Can look almost like anything.
    • Like it is said that sarcoidosis is in every internal medicine DDx... melanoma is every pathologic DDx
  • May have no nuclear atypia.
    • Diagnosis is based on architecture (upward spread in the epidermis, single cells, asymmetry).

DDx

Images:

Skin

Features (skin):

  1. Melanocytic differentiation:
    • Pigmentation (melanin).
    • Nuclear pseudoinclusion.
    • Gray cytoplasm.
    • Clear (artefactual) halo around cells.
  2. Architecture:
    • Sheeting - diagnostic.
    • Asymmetry - as judged from low power magnification.
  3. Lack of maturation - see below.
  4. +/-Nuclear atypia - esp. nucleoli.
  5. +/-Upward scatter of melanocytes AKA intraepidermal ascent - "cannonball" appearance.
    • No diagnostic significance in the following cases:
      • Acral sites - see: Acral nevus.
      • Histologic evidence of trauma.
        • Thick dense stratum corneum.

Maturation - with depth:

  • Nests get smaller.
  • Cells get smaller.
  • Mitoses decrease.
  • Pigmentation decrease.

DDx:

Images:

Regression of melanoma

General
  • Complete regression without metastases estimated to be 10-20%.[1]
    • Common ~25% of cases.[1]
  • Complete regression and partial regression >75% of the lesion are a poor prognostic feature.[2]
Microscopic

Features - all required:

  • No melanocytes.
  • Melanophages.
  • Fibrosis.
  • Thinned epidermis.
  • Telangiectatic vessels.
  • Lymphocytes.

Metastatic versus primary

Primary lesions should have:

  • Epidermal involvement.

Metastatic lesions classically have:

  • Tumour angiotropism (tumours cells cluster around vessels).
  • Intravascular invasion.
  • No epidermal component.

Note:

  • Histology is not definitive for metastatic melanoma vs. primary melanoma; epidermal involvement may be seen in mets.
    • History/clinical is important for differentiation.

Breslow thickness

  • AKA maximum tumour thickness.
  • Depth measured from stratum granulosum to deepest intradermal tumour cell - predictive of survival.[3]

Clark level

  • AKA anatomic level.
  • Not as reproducible as Breslow thickness - not used.

Anatomic level - definition:

  • I = epidermis only (AKA melanoma in situ).
  • II = extends into papillary dermis but does not fill or expand.
  • III = fills and expands papillary dermis.
  • IV = extends into reticular dermis.
  • V = extends into subdermis.

Subtypes

Subtype name Key feature Microscopic additional DDx Image Notes/other
Melanoma in situ confined to epidermis, nuclear atypia melanocyte enlargement, nuclear hyperchromasia, +/- melanocytes above suprapapillary plate (above basal layer) = "Pagetoid spread" melanocytic hyperplasia, pagetoid Spitz nevus (upmc.edu) lentigo maligna is melanoma in situ[4] on sun damaged skin
Malignant melanoma - superficial spreading type atypical melanocytes at all levels of epidermis + dermis atypical dermal melanocytes single, in cluster or sheets compound melanocytic nevus Image? Notes/other?
Malignant melanoma - lentiginous type atypical melanocytes prominent along basal keratinocytes + in dermis nuclear atypia DDx? Image? Notes/other?
Malignant melanoma - nodular type dermal large nodule/sheet nuclear atypia; may not be prominent in epidermis metastatic melanoma Image? Notes/other?
Malignant melanoma - desmoplastic-neurotropic type AKA desmoplastic melanoma large atypical spindle cells, btw collagen predominantly dermal pleomorphic undifferentiated sarcoma (MFH), scar, dermatofibroma, DFSP, leiomyosarcoma, desmoplastic Spitz nevus, sclerosing blue nevus (upmc.edu) IHC: rarely S100-, generally Melan A- & HMB-45-; subdivided into mixed desmoplastic melanoma and pure desmoplastic melanoma
Malignant melanoma - nevoid type prominent nucleoli, deep mitoses - high power diagnosis mimics nevus at low power; "push" elastic fibers downward (unlike benign nevi) (benign) nevus Image? deep HMB-45+
Malignant melanoma - spitzoid type nested pattern, nuclear atypia, no maturation (large deep cells) NC ratio increased (vs. Spitz) Spitz nevus Image? Notes/other?

Subtypes in short

Subtype name Key feature
in situ confined to epidermis, unlike all others
superficial spreading above basal layer
lentiginous along basal keratinocytes
nodular nodular dermal lesion
desmoplastic-neurotropic atypical dermal spindle cells
nevoid nevus-like at low power
spitzoid mimics Spitz nevus (at DE junction)

Electron microscopy

  • Melanosomes.

Image(s):

Stains

  • Fontana-Masson stain, stains melanin.[5]
    • May be useful to differentiate melanin from other brown stuff (e.g. lipofuscin, hemosiderin).

IHC

Standard panel:

  1. S100 +ve.
    • Negative staining pretty much excludes the diagnosis.
  2. HMB-45 +ve -- esp. deep.
  3. Melan A (MART-1) +ve.

Others:

  • SOX10 +ve -- useful for diff. from excision scar.[6]
    • SOX-10 = pan-schwannian and melanocytic marker.

Notes:

  • The standard panel above (S100, HMB-45, MART-1) is also positive in other lesions, e.g. cellular blue nevus.

See also

References

  1. ↑ 1.0 1.1 Printz, C. (Jul 2001). "Spontaneous regression of melanoma may offer insight into cancer immunology.". J Natl Cancer Inst 93 (14): 1047-8. PMID 11459861.
  2. ↑ Crowson, AN.; Magro, CM.; Mihm, MC. (Feb 2006). "Prognosticators of melanoma, the melanoma report, and the sentinel lymph node.". Mod Pathol 19 Suppl 2: S71-87. doi:10.1038/modpathol.3800517. PMID 16446717.
  3. ↑ Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 595. ISBN 978-1416054542.
  4. ↑ McKenna, JK.; Florell, SR.; Goldman, GD.; Bowen, GM. (Apr 2006). "Lentigo maligna/lentigo maligna melanoma: current state of diagnosis and treatment.". Dermatol Surg 32 (4): 493-504. doi:10.1111/j.1524-4725.2006.32102.x. PMID 16681656.
  5. ↑ URL: http://education.vetmed.vt.edu/curriculum/VM8054/labs/Lab2/Examples/exfontana.htm. Accessed on: 5 May 2010.
  6. ↑ Ramos-Herberth FI, Karamchandani J, Kim J, Dadras SS (September 2010). "SOX10 immunostaining distinguishes desmoplastic melanoma from excision scar". J. Cutan. Pathol. 37 (9): 944–52. doi:10.1111/j.1600-0560.2010.01568.x. PMID 20653825.
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