Melanoma pathophysiology: Difference between revisions

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==Pathophysiology==
==Pathophysiology==
[[Image:Malignant melanoma.jpg|left|thumb|240px|Nodular melanoma on the leg of an elderly woman.]]
===Molecular Pathogensis===
 
*The development of melanoma first begins with the disruption of nevus growth control.
Generally, an individual's risk for developing melanoma depends on two groups of factors: intrinsic and environmental.<ref>[http://www.skincarephysicians.com/skincancernet/who_is_most.html  Who is Most at Risk for Melanoma?]</ref> "Intrinsic" factors are generally an individual's family history and inherited [[genotype]], while the most relevant environmental factor is sun exposure.
 
[[Epidemiologic]] studies suggest that exposure to [[ultraviolet]] radiation (UVA<ref name="uva">{{cite journal | author = Wang S, Setlow R, Berwick M, Polsky D, Marghoob A, Kopf A, Bart R | title = Ultraviolet A and melanoma: a review. | journal = J Am Acad Dermatol | volume = 44 | issue = 5 | pages = 837-46 | year = 2001 | id = PMID 11312434}}</ref> and UVB) is one of the major contributors to the development of melanoma. UV radiation causes [[DNA damage|damage]] to the [[DNA]] of cells, typically thymine dimerization, which when unrepaired can create [[mutation]]s in the cell's [[gene]]s. When the cell [[cell division|divides]], these mutations are propagated to new generations of cells. If the mutations occur in [[oncogene]]s or [[tumor suppressor gene]]s, the rate of [[mitosis]] in the mutation-bearing cells can become uncontrolled, leading to the formation of a [[tumor]]. Occasional extreme sun exposure (resulting in "[[sunburn]]") is causally related to melanoma.<ref>{{cite journal | author = Oliveria S, Saraiya M, Geller A, Heneghan M, Jorgensen C | title = Sun exposure and risk of melanoma. | journal = Arch Dis Child | volume = 91 | issue = 2 | pages = 131-8 | year = 2006 | id = PMID 16326797}}</ref> Those with more chronic long term exposure (outdoor workers) may develop protective mechanisms. Melanoma is most common on the back in men and on legs in women (areas of intermittent sun exposure) and is more common in indoor workers than outdoor workers (in a British study<ref>{{cite journal | author = Lee J, Strickland D | title = Malignant melanoma: social status and outdoor work. | journal = Br J Cancer | volume = 41 | issue = 5 | pages = 757-63 | year = 1980 | id = PMID 7426301}}</ref>). Other factors are [[mutation]]s in or total loss of [[tumor suppressor gene]]s.  Use of sunbeds (with deeply penetrating UVA rays) has been linked to the development of skin cancers, including melanoma.
===[[Superficial spreading melanoma]]===
 
===Genetics===
===Genetics===
Familial melanoma is genetically heterogeneous,<ref>{{cite journal | author = Greene MH. | title = The genetics of hereditary melanoma and nevi. | journal = Cancer | volume = 86 | issue = 11 | pages = 2464-2477 | year = 1998 | id = PMID 10630172}}</ref> and loci for familial melanoma have been identified on the chromosome arms 1p, 9p and 12q. Multiple genetic events have been related to the pathogenesis of melanoma.<ref>{{cite journal | author = Halachmi S, Gilchrest BA. | title = Update on genetic events in the pathogenesis of melanoma. | journal = Curr Opin Oncol | volume = 13 | issue = 2 | pages = 129-136 | year = 2001 | id = PMID 11224711}}</ref> The multiple [[Tumor suppressor gene|tumor suppressor]] 1 (CDKN2A/MTS1) gene encodes p16INK4a - a low-molecular weight protein inhibitor of [[cyclin-dependent kinase|cyclin-dependent protein kinases]] (CDKs) - which has been localised to the p21 region of [[Chromosome 9 (human)|human chromosome 9]].<ref>[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=gene&cmd=Retrieve&dopt=full_report&list_uids=1029 CDKN2A cyclin-dependent kinase inhibitor 2A (melanoma, p16, inhibits CDK4)] from Entrez Gene</ref>
<p>Today, melanomas are diagnosed only after they become visible on the skin.  In the future, however, physicians will hopefully be able detect melanomas based on a patient’s [[genotype]], not just his or her [[phenotype]].  Recent genetic advances promise to help doctors to identify people with high-risk genotypes and to determine which of a person’s lesions have the greatest chance of becoming cancerous.
<p>A number of rare mutations, which often run in families, are known to greatly increase one’s susceptibility to melanoma.  One class of mutations affects the gene [[CDKN2A]].  An alternative reading frame mutation in this gene leads to the destabilization of [[p53]], a [[transcription factor]] involved in [[apoptosis]] and in fifty percent of human cancers.  Another mutation in the same gene results in a non-functional inhibitor of [[CDK4]], a [cyclin-dependent kinase] that promotes cell division.  Mutations that cause the skin condition [[Xeroderma Pigmentosum]] (XP) also seriously predispose one to melanoma.  Scattered throughout the genome, these mutations reduce a cell’s ability to repair DNA.  Both CDKN2A and XP mutations are highly penetrant.
<p>Other mutations confer lower risk but are more prevalent in the population.  People with mutations in the MC1R gene, for example, are two to four times more likely to develop melanoma than those with two wild-type copies of the gene.  [[MC1R]] mutations are very common; in fact, all people with red hair have a mutated copy of the gene. 
Two-gene models of melanoma risk have already been created, and in the future, researchers hope to create genome-scale models that will allow them to predict a patient’s risk of developing melanoma based on his or her genotype.


==Pathology==
==Pathology==

Revision as of 19:03, 21 August 2015

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

Pathophysiology

Molecular Pathogensis

  • The development of melanoma first begins with the disruption of nevus growth control.

Genetics

Pathology

Common Subclasses Features on Gross Pathology Features on Histopathological Microscopic Analysis
Superficial spreading melanoma
  • Brown/black color, but may include reddish brown or white
  • Hyperkeratotic, diffused borders with no distinct demarcation
  • Irregular and elevated
  • Presence of intraepidermal lateral spread (most characteristic feature)
  • Dermal invasion
  • Desmoplasia
  • Epidermal hyperplasia
  • Appearance of epithelioid cells with occasional spindle cells
Nodular melanoma
  • Tan/reddish brown color
  • Sharp borders
  • Well-demarcated, dome-shaped papular/verruccous lesion
  • Sharp border differentiating malignant vs. normal tissue due to absence of intraepidermal lateral spread / no radial growth plate (most characteristic feature)
  • Appearance of epithelioid cells with occasional spindle cells
  • Melanocytes may have absent/minimal pigmentation
Acral lentiginous melanoma
  • Brown/black color, but may include reddish brown or white
  • Hyperkeratotic, diffused borders with no distinct demarcation
  • Irregular and elevated
  • Epidermal acanthosis and hyperkeratosis (mmost characteristic feature)
  • Malignant melanocytes spread along the basal layer
  • Cells arranged in lentiginous and dycohesive pattern along the dermoepidermal junction
  • May be any of round, epithelioid, spindle, or oval cells
  • May have perineural or endoneural invasion
Lentigo maligna melanoma
  • Brown/black color, but may include reddish brown or white
  • Hyperkeratotic, diffused borders with no distinct demarcation
  • Irregular and elevated
  • Epidermal atrophy and flattening and prominent dermal invasion (most charactersitic feature)
  • Large, pleomorphic cells
  • Cells arranged in lentiginous and dycohesive pattern along the dermoepidermal junction
  • Preservation of retiform epidermis
  • May be any of round, epithelioid, spindle, or oval cells
  • Evidence of actinic damage of the dermal matrix
  • May have perineural or endoneural invasion
  • Positivity for CD133+ and CD34+
Non-cutaneous melanoma
  • Variable morphology depending on location of melanoma
  • Histopathologically similar to other subtypes of melanoma
Dermoplastic/Spindle cell melanoma
  • Skin colored and morphologically resembles scar tissue
  • Dermal, fibrotic nodule
  • Ill-defined, variable spindle cells with irregular contours and stromal desmoplasia
  • Highly infiltrative pattern
  • Appearance of sclerotic collagen fibers
  • Nuclear hyperchromasia
  • Appearance of lymphoid aggregates
  • Solar elastosis
  • Involvement of endoneurium and perineurium (neurotropism)
  • Possibly evidence of other melanoma subtypes (co-existing tumors, especially lentiginous melanoma)"
Nevoid melanoma
  • Morphologically similar to a melanocytic nevus
  • Dermal mitosis
  • Hypercellular and monomorphous-appearing dermal melanocytes that have a characteristic sheet-like appearance
  • Evidence of cytologic atypia (nuclear enlargement, pleomorphism, irregular nuclear membrane, hyperchromasia)
  • Irregular basal infiltration
  • Evidence of angiotropism
Spitzoid melanocytic neoplasm
  • Morphologically similar to a Spitz nevus
  • Appearance of melanocytic proliferation along with features of Spitz tumors (small diametes, well-demarcated, symmetric lesion with no ulceration, epidermal effacement, dermal mitosis, or involvement of the subcutaneous fat)
  • May have features that are not typically characteristic of Spitz tumors (ulceration, poor demarcation)
  • Vertically oriented spindled melanocytes
  • Clefts between junctional melanocytes
Angiotropic melanoma
  • No gross morphological features that distinguish angiotropic melanoma from other subtypes of melanoma
  • Melanoma cells in close proximity to abluminal surfaces of blood and/or lymphatic channels
  • No invasion within the vascular lamina itself
Blue nevus-like melanoma
  • Morphologically similar to a blue nevus
  • Asymmetric nodular/multinodular appearance
  • Aggregates of melaninized, atpical spindle cells
Composite melanoma

Features of more than one subtype on gross pathology

  • Features of more than one subtype on microscopic analysis
  • May be characterized by one of the following:
  • Collision tumor: Collision of melanoma and another nearby malignant tumor
  • Colonization: Colonization of melanocytes in a tumor
  • Combined: Two distinct tumors appear to have mixed features of the melanoma and the other tumor
  • Biphenotypic: One tumor that has features of melanoma and another epithelial malignancy

References