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63. Melanocytic lesions (+ introduction to skin lesions): Difference between revisions

63. Melanocytic lesions (+ introduction to skin lesions) (view source)

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Melanoma is a highly malignant tumor arising from melanocytes. It is the most common cause of death from dermatological diseases. It’s caused by UV radiation-mediated DNA damage, so the risk factors are excessive sunlight exposure and conditions that predispose to increased sunlight exposure or decreased defence against this type of DNA damage.
Melanoma is a highly malignant tumor arising from melanocytes. It is the most common cause of death from dermatological diseases. It’s caused by UV radiation-mediated DNA damage, so the risk factors are excessive sunlight exposure and conditions that predispose to increased sunlight exposure or decreased defence against this type of DNA damage.


Risk factors:
=== Risk factors ===
 
* Excessive exposure to UV radiation (much sun, little sunscreen)
* Excessive exposure to UV radiation (much sun, little sunscreen)
* Light skin
* Light skin
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Very few dysplastic nevi transform into melanoma; most cases of melanoma arise de novo. Because of this, sporadic dysplastic nevi don’t increase the risk significantly for developing melanoma. Dysplastic nevus syndrome however has an almost 100% risk of developing into melanoma.
Very few dysplastic nevi transform into melanoma; most cases of melanoma arise de novo. Because of this, sporadic dysplastic nevi don’t increase the risk significantly for developing melanoma. Dysplastic nevus syndrome however has an almost 100% risk of developing into melanoma.


Pathogenesis: Melanoma is characterised by two different growth phases; the radial growth phase and the vertical growth phase.
=== Pathogenesis ===
Melanoma is characterised by two different growth phases; the radial growth phase and the vertical growth phase.


During the radial/horizontal growth phase, the tumor grows horizontally along the epidermis, corresponding to an ''in situ'' lesion. During this phase the tumor cells don’t have the capacity to metastasize.
During the radial/horizontal growth phase, the tumor grows horizontally along the epidermis, corresponding to an ''in situ'' lesion. During this phase the tumor cells don’t have the capacity to metastasize.
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During the vertical growth phase, the tumor grows vertically into the dermis. It is during this phase that the tumor cells acquire the ability to metastasize. It is the extent of the vertical growth phase that determines the biological behaviour and prognosis.
During the vertical growth phase, the tumor grows vertically into the dermis. It is during this phase that the tumor cells acquire the ability to metastasize. It is the extent of the vertical growth phase that determines the biological behaviour and prognosis.


Subtypes: Multiple subtypes of melanoma exist:
=== Subtypes ===
Multiple subtypes of melanoma exist:


Superficial spreading melanoma is the most common subtype. It’s characterised by a long radial growth phase and mostly superficial spreading.
Superficial spreading melanoma is the most common subtype. It’s characterised by a long radial growth phase and mostly superficial spreading.
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Acral lentiginous melanoma is the least common type. Its radial growth phase is slow. It occurs on the palms or soles of dark-skinned individuals. Unlike the other subtypes this type is not related to UV exposure.
Acral lentiginous melanoma is the least common type. Its radial growth phase is slow. It occurs on the palms or soles of dark-skinned individuals. Unlike the other subtypes this type is not related to UV exposure.


Diagnosis: The ABCDE criteria are useful for distinguishing between benign skin lesions and melanoma:
=== Diagnosis ===
The ABCDE criteria are useful for distinguishing between benign skin lesions and melanoma:


* A – asymmetric shape
* A – asymmetric shape
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Melanomas can also bleed and itch, which benign melanocytic lesions don’t do. Hair never grows out of melanomas.
Melanomas can also bleed and itch, which benign melanocytic lesions don’t do. Hair never grows out of melanomas.


Two staging systems are important in melanoma. The most important is the Breslow depth, which measures the length in millimetres from the stratum granulosum to the deepest part of the tumor. Tumors of just a few mm (2 – 4) have significantly poorer prognosis than those that are 1 – 2 mm.
Two staging systems are important in melanoma. The most important is the Breslow depth, which measures the length in millimetres from the stratum granulosum to the deepest part of the tumor. The prognosis worsens considerably with increase in depth; tumors of just a few mm (2 - 4) have significantly poorer prognosis than those that are 1 - 2 mm.


The other staging system is the Clark level, which ranges from I to V. At level I the tumor is in situ, and at level V the tumor has invaded the subcutaneous tissue. The Breslow depth has proven to be of higher prognostic value than the Clark level.
The other staging system is the Clark level, which ranges from I to V. At level I the tumor is in situ, and at level V the tumor has invaded the subcutaneous tissue. The Breslow depth has proven to be of higher prognostic value than the Clark level.


Prognosis: The survival rate drops in cases where metastases are present at the time of diagnosis. Melanoma frequently metastasizes into the liver, lung, brain and bone. Rarely, melanoma can metastasize into unusual locations like the heart and gallbladder. These metastases have characteristic black pigmentation.
=== Prognosis ===
Increased Breslow depth means worse prognosis. The survival rate also drops in cases where metastases are present at the time of diagnosis. Melanoma frequently metastasizes into the liver, lung, brain and bone. Rarely, melanoma can metastasize into unusual locations like the heart and gallbladder. These metastases have characteristic black pigmentation.


The prognosis is poorer in tumors that have penetrated the dermis.
The prognosis is poorer in tumors that have penetrated the dermis.
[[Category:Pathology 2 - Theoretical exam topics]]
[[Category:Pathology 2 - Theoretical exam topics]]