Melanoma – Reference Corson, John D. “Surgery” Chap 7.15.4-7.15.5. Mosby. 2001. & Cameron, J.L. Current Surgical Therapy. Mosby. 2001. Pp 1209-1212.
Incidence: Deliberate sunbathing has resulted in doubled incidence every 10 years, highest 40/100,000 in Queensland, Australia. Death rates remain constant despite increased incidence. Women 2x affected as men. Common among high socioeconomic groups.
Etiology: Intense solar radiation exposure unequivocal risk factor. May occur in non-exposed areas. 1 proposed mechanism is prolonged exposure may compromise the immune response to abnormal melanocyctic growth in the genetically susceptible individuals.
Classification: 4 major types
· Superficial spreading: most common (50-70%). Large flat pigmented lesion. Demonstrates radial, intraepidermal growth for years, called Radial Growth Phase. Eventually tumor transforms into invasive disease, called Vertical Growth Phase with stronger tendency to metastasize.
· Nodular: 10-15% melanomas. Small raised nodule +/- pigmentation. May ulcerate. Demonstrated vertical growth from outset, therefore more invasive and higher potential for metastasis.
· Lentigo malignant: 10%. Melanoma arising in a pre-existing lentigo maligna, which is a large flat brown lesion with varying depths of pigmentation occurring commonly in elderly. Long radial growth phase of 10-25 years.
· Acral lentiginous: 5-10% melanomas. Prolonged radial growth intermediate between superficial spreading and lentigo malignant. Occurs on plantar or palmar skin or subungual locations. Variations in pigmentation. Can grow very large. Once vertical growth occurs, metastasis develops quickly.
Spread: local invasion, lymphatic, hematogenous. Satellitosis is appearance of numerous cutaneous deposits of metastatic melanoma around primary or previously removed lesion. In Transit metastasis presents as palpable subcutaneous tumor nodules along the path of normal lymphatic drainage.
|
Breslow thickness |
5-year survival % |
|
<1.5 |
92.5 |
|
1.5-3.49 |
72.6 |
|
>3.49 |
48 |
|
Staging:
Thickness of primary tumor is the single most important prognostic feature!
Measure by Breslow thickness & Clark Level.
|
Thickness of
melanoma |
Excision Margin |
|
Melanoma in situ |
5mm |
|
<1mm |
1cm |
|
1-4mm |
2cm |
|
>4mm |
³2cm |
Management: Biopsy, excisional if possible, punch if needed (never shave). Margins as above. Sentinel node biopsy for melanomas >1mm or those that are smaller but with poor prognostic features. Lymphadenectomy for nodal disease offers survival benefit if no distant metastasis present.