Melanoma in situ

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Author: Mikael Häggström [notes 1]
Melanoma of the skin generally presents as a dark skin focality and/or a suspected malignant skin excision.

Fixation

Generally 10% neutral buffered formalin.

See also: General notes on fixation

Gross processing

Gross examination

Note:

  • Color
  • Well-defined or diffuse border
  • Size
  • Any elevation

Tissue selection

Tissue selection from suspected malignant skin lesions, by lesion size:[1][notes 2]
<4 mm 4 - 8 mm 9 - 15 mm
Tissue selection from skin excision with less than 4 mm suspected malignant lesion.png Tissue selection from skin excision with 4-8 mm suspected malignant lesion.png Tissue selection from skin excision with 9-15 mm suspected malignant lesion.png

In table above, each top image shows recommended lines for cutting out slices to be submitted for further processing. Bottom image shows which side of the slice that should be put to microtomy. Dashed lines here mean that either side could be used.

Further information: Gross processing of skin excisions

Microscopic evaluation

Differential diagnoses

Distinguish mainly from dysplastic nevus and invasive melanoma of the skin:

Dysplastic nevus

Comparison of congenital pattern nevus, dysplastic nevus and suspected melanoma   edit
Parameter Non-atypical congenital pattern Low-grade dysplastic nevus High-grade dysplastic nevus Suspected melanoma in situ
Mild dysplasia Moderate dysplasia Severe dysplasia
Macroscopic Lateral circumscription[2] Sharp Slightly diminished Moderate Poor
Excised melanoma in situ.jpg
Symmetry[2] Good Often broken Rare
Structural
(Low
mag.)
Delimitation[3] Rarely diffuse Sometimes diffuse Often diffuse
Lentiginous proliferation[notes 3][3] Yes, along with rete pegs Yes, along with and focally between rete pegs Yes, along with and focally between rete pegs Yes partially continuous, multilayered
Histopathology of lentigo maligna.jpg
Bridging[3] Rarely Often
Confluent nests[3] Rarely Sometimes Often Often widespread
Pigment distribution[3] Regular Irregular
Suprabasal presence (less than most superficial third of subcorneal epidermis) Occasionally centrally[2] No[3] or rarely[2] Occasionally centrally[2] Yes, multifocal[3]
Pagetoid migration including superficial third of subcorneal epidermis[3] No No Yes, in a maximum of 2 HPF centrally, but not peripherally Yes, multifocal and/or in periphery
Peripheral.
Extended rete pegs Ocassional[2] Yes, regular[3] Yes, varying[3] Yes, often irregular[3] Varying, flattened[3]
Concentric fibrosis Regressive[2] Yes[3] Occasional[2]
Lamellar fibrosis Rarely[3] Often[3] Often pronounced[3] Occasional[2]
Lymphocytic infiltrate[3] Mild, perivascular Mild or moderate, perivascular Varying Varying
Suprapapillary plate involvement No[2] Usually no[2] Often[2] Yes[2]
Cellular
(high
mag.)
Junctional extension[2] Unusual Usual Extensive
Nuclear size[2] Age-related Small Medium Large Medium or large. Pleomorphic[4]
Nuclear pleomorphism[5] Slight Prominent
Chromatin pattern Uniform[2] Condensed[2] Partically expanded[2] Expanded, coarse in some cells[2] Expanded, hyperchromatic, coarse.[2] Usually granular.[5]
Nucleoli[2] Age-related Small Medium Large Usually[5] large
Mitoses[2] Few superficial Superficial and deep
Histological regression[5][notes 4] Usually Usually not
Percentage of atypical melanocytes[3] <10% About 10 - 50% about 50-90% Usually> 90%
Intradermal melanocytic atypia[3] No Rarely, in superficial part Can be detected in superficial part
Intradermal melanocyte maturation[3] Yes Yes, can be partial Yes, can be partial Variable

In suspected but not certain nevus or melanoma in situ, generally perform immunohistochemistry with SOX10, whereby melanocyte proliferation and nuclear pleomorphism is easier to see.[notes 5]

Further information: Evaluation of suspected malignancies

Invasive melanoma of the skin

Invasive melanoma of the skin has features melanoma in situ, but also has dermal involvement of atypical melanocytes with cytologic atypia and no maturation.[6]

Further workup

Upon a diagnosis of melanoma in situ, evaluate its margins.
Optionally, attempt to determine the histopathologic type and amount of cytoplasmic pigmentation:

Margins

If melanoma, determine if the distance to any margin is greater or lesser than 2-3 mm.

  • 2 mm is used as a cutoff for sharply demarcated, small, superficially spreading or nevoid melanomas.[7]
  • 3 mm is used for ill-defined lentigo maligna melanoma in situ.[7]

If lesser, quantify the distance.

If margins are difficult to determine, consider immunohistochemistry with SOX10 to better visualize melanoma nests.[notes 5]

Histopathologic type

Main types of melanoma in situ are:

Type Features Micrograph
Superficial spreading melanoma in situ Melanoma cells with nest formation along the dermo-epidermal junction. Histopathology of superficial spreading melanoma.jpg
Lentigo maligna Linear spread of atypical epidermal melanocytes along stratum basale.[8]
Histopathology of lentigo maligna.jpg
Acral lentiginous melanoma in situ Continuous proliferation of atypical melanocytes at the dermoepidermal junction.[9] Histopathology of acral lentiginous melanoma in situ, intermediate magnification.jpg
Cytoplasmic pigmentation

Optionally, estimate the cytoplasmic pigmentation of melanocytes:[10]

Report

Most important entries:

  • Melanoma area dimensions (width x width)[11]
  • Radicality,[11] mainly into either of the following: edit
  • >2 or 3 mm (as per Further workup above): "Clear margins".[notes 6]
  • <2 or 3 mm but not continuous with edge: "Close margins at __ mm at (location)[notes 7]." Numbers are generally given at an exactness of 0.1 mm.
  • Continuous with margin: "Not radically excised at (location)[notes 7]."
See also: General notes on reporting

Notes

  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.
  2. The excision example shows a superficial basal cell carcinoma.
  3. Lentiginous proliferation is proliferation along the basal layer of the epidermis
  4. Histological regression is one or more areas within a tumor in which neoplastic cells have disappeared or decreased in number. In this case, this means complete or partial disappearance from areas of the dermis (and occasionally from the epidermis), which have been replaced by fibrosis, accompanied by melanophages, new blood vessels, and a variable degree of inflammation.
    - Ribero, Simone; Gualano, Maria Rosaria; Osella-Abate, Simona; Scaioli, Giacomo; Bert, Fabrizio; Sanlorenzo, Martina; Balagna, Elena; Fierro, Maria Teresa; et al. (2015). "Association of Histologic Regression in Primary Melanoma With Sentinel Lymph Node Status ". JAMA Dermatology 151 (12): 1301. doi:10.1001/jamadermatol.2015.2235. ISSN 2168-6068. 
  5. 5.0 5.1 SOX10 stains cell nuclei of melanocytes.
    - Miettinen, Markku; McCue, Peter A.; Sarlomo-Rikala, Maarit; Biernat, Wojciech; Czapiewski, Piotr; Kopczynski, Janusz; Thompson, Lester D.; Lasota, Jerzy; et al. (2015). "Sox10—A Marker for Not Only Schwannian and Melanocytic Neoplasms But Also Myoepithelial Cell Tumors of Soft Tissue ". The American Journal of Surgical Pathology 39 (6): 826–835. doi:10.1097/PAS.0000000000000398. ISSN 0147-5185. 
  6. A more comprehensive report may state "Clear margins at over __ mm" or the value thereof if it has been measured more exactly.
  7. 7.0 7.1 Locations are mainly the deep edge, or the (superior/inferior/medial/lateral) radial edge.

References

  1. There are many variants for the processing of skin excisions. These examples use aspects from the following sources: ". Ochsner J 5 (2): 22–33. 2003. PMID 22826680. PMC: 3399331. Archived from the original. . 
    - With a "standard histologic examination" that, in addition to the lesion, only includes one section from each side along the longest diameter of the specimen.
    - It also shows an example of circular coverage, with equal coverage distance in all four directions.
    - The entire specimen may be submitted if the risk of malignancy is high.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 Arumi-Uria, Montserrat; McNutt, N Scott; Finnerty, Bridget (2003). "Grading of Atypia in Nevi: Correlation with Melanoma Risk ". Modern Pathology 16 (8): 764–771. doi:10.1097/01.MP.0000082394.91761.E5. ISSN 0893-3952. 
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 Katarzyna Lundmark, Britta Krynitz, Ismini Vassilaki, Lena Mölne, Annika Ternesten Bratel. Histopatologisk bedömning och gradering av dysplastiskt nevus samt gränsdragning mot melanom in situ/melanom (Histopathological assessment and grading of dysplastic nevus and distinction from melanoma in situ/melanoma). KVAST (Swedish Society of Pathology). Retrieved on 2019-09-18.
  4. Christopher S. Hale. Skin melanocytic tumor - Melanoma - Invasive melanoma. Topic Completed: 1 May 2013. Revised: 17 September 2019
  5. 5.0 5.1 5.2 5.3 Husain, Ehab A; Mein, Charles; Pozo, Lucia; Blanes, Alfredo; Diaz-Cano, Salvador J (2011). "Heterogeneous topographic profiles of kinetic and cell cycle regulator microsatellites in atypical (dysplastic) melanocytic nevi ". Modern Pathology 24 (4): 471–486. doi:10.1038/modpathol.2010.143. ISSN 0893-3952. 
  6. Christopher S. Hale. Skin melanocytic tumor - Melanoma - Invasive melanoma. Pathology Outlines. Topic Completed: 1 May 2013. Revised: 17 September 2019
  7. 7.0 7.1 Measurements used to classify a melanoma as radical: Page 406 in: Klaus J. Busam, Richard A Scolyer, Pedram Gerami (2018). Pathology of Melanocytic Tumors . Elsevier Health Sciences. ISBN 9780323508681. 
  8. Error on call to Template:cite web: Parameters url and title must be specifiedHon A/Prof Amanda Oakley (2011). . DermNet NZ.
  9. Piliang, Melissa Peck (2009). "Acral Lentiginous Melanoma ". Surgical Pathology Clinics 2 (3): 535–541. doi:10.1016/j.path.2009.08.005. ISSN 18759181. 
  10. Rees, Jonathan; Viros, Amaya; Fridlyand, Jane; Bauer, Juergen; Lasithiotakis, Konstantin; Garbe, Claus; Pinkel, Daniel; Bastian, Boris C (2008). "Improving Melanoma Classification by Integrating Genetic and Morphologic Features ". PLoS Medicine 5 (6): e120. doi:10.1371/journal.pmed.0050120. ISSN 1549-1676. 
  11. 11.0 11.1 . An Example of a Melanoma Pathology Report. Melanoma Foundation. Retrieved on 2019-09-24.