Melanoma is the proliferation of atypical melanocytes. It is the most dangerous type of skin cancer. Melanoma has a high potential to invade the dermis and metastasise. 70% of melanoma arises from normal skin, while 30% arise from pre-existing naevi. In women, they are common on the lower leg; they present sooner since women are more concerned about skin lesions. They commonly occur on the back in men. Survival is inversely correlated to the depth of invasion (Clark’s levels or Breslow thickness)
Melanoma accounts for only 1% of skin cancer, but it is a major cause of mortality from skin cancer. The peak age is 40 – 70 years old – it is still a significant cause of cancer in young individuals.
Types of melanoma
| Type of melanoma | Description |
|---|---|
| Superficial spreading melanoma (65%) | Occurs on the face and neck (or other sun-exposed areas) in elderly patients. Typically a large, flat, dark lesion. Has the best prognosis |
| Lentigo maligna melanoma (15%) | Occurs on the face and neck (or other sun-exposed areas) in elderly patients. Typically, a large, flat, dark lesion. Has the best prognosis |
| Nodular melanoma (10 – 15%) | Occurs anywhere on the body, often dark coloured. May be pearly or lack pigment. Rarely metastasizes but grows rapidly in a vertical direction. This has the worst prognosis. |
| A rarer type common in Africans (dark-skinned individuals). Occurs on the palms, soles or subungal skin (under fingernails) | A rarer type common in Africans (dark-skinned individuals). Occurs on the palms or soles or subungal skin (under fingernails) |
Growth of melanoma
| Growth | Description |
|---|---|
| In situ | Tumour spreads into the dermis |
| Invasive | Tumur spreads into the dermis |
| Metastatic | Tumour spread to other tissues |
Clark’s level (anatomic level of skin invasion)
| Clark’s level | Description |
|---|---|
| Level I | Confined to epidermis (melanoma in situ) |
| Level II | Invades papillary dermis |
| Level III | Fills papillary dermis |
| Level IV | Invades reticular dermis |
| Level V | Invades subcutaneous tissue |
Brewslow thickness (vertical depth of tumour in millimetres; it is the most important prognostic factor for localised melanoma)
| Breslow Thickness (mm) | Tumor Category (T stage) | Prognostic Significance |
|---|---|---|
| ≤ 1.0 mm | T1 | Thin melanoma, best prognosis |
| 1.01 – 2.0 mm | T2 | Intermediate risk |
| 2.01 – 4.0 mm | T3 | Higher risk of metastasis |
| > 4.0 mm | T4 | High risk, poorest prognosis |
- Risk factors for melanoma
- Sun exposure (not as significant as SCC or BCC)
- Male gender
- Advanced age
- Multiple naevia (> 50 is a significant risk)
- Family history of melanoma (p16 loss of function)
- Fair complexion
- Smoking
- History of melanoma or other skin cancer
- Dysplastic nevus syndrome (autosomal dominant)
- Pathophysiology
- 50 – 70% of melanomas arise de novo; the rest present at the site of existing moles.
- Physical examination
- Asymmetric
- Irregular Borders
- Variegated Color
- Diameter > 6mm
- Evolving
- Pigmented lesion
- Differentials
- Benign melanocytic naevus (mole)
- Lentigines and ephelides
- Seborrhoeic keratoses
- Dermatofibroma
- Pigmented basal cell carcinoma
- Investigations
- Dermoscopy to visualise the lesion
- Atypical pigment network
- Aggregated black or brown dots and globules
- Parallel ridge pattern on palms and soles
- Full-thickness excisional biopsy (with narrow clinical margins)
- Nests of melanocytes
- Prominent nucleoli
- Mitotic figures
- Tumour marker S100
- Metastatic workup: whole-body and brain contrast-enhanced CT scan for stage IIB; staging CT for stage IIC to IV; brain MRI
- Dermoscopy to visualise the lesion
- Treatment
- Wide local excision – margins are guided by depth
- Melanoma in situ: 5 mm margin
- < 1mm depth: 10 mm margin
- 1 – 4 mm depth: 10 – 20 mm margin
- 4 mm depth: 20 mm margin
- Sentinel lymph node biopsy
- For melanoma with Breslow thickness of 0.8 – 1.0 mm with ulceration, lymphvascular invasion or mitotic index of 2 or more
- For melanoma with a Breslow thickness > 1.0 mm
- Targeted therapy with BRAF and MEK inhibitors
- Immunotherapy – anti-PD-1 +/- CTLA-4 therapy – for advanced disease
- Chemotherapy or radiotherapy for advanced lymphoma
- Wide local excision – margins are guided by depth
- Complications
- Local tissue invasion and destruction
- Prognosis
- Prognosis is based on the depth of dermal invasion (Breslow depth) for local melanoma
- Breslow depth measures the uppermost cell in the stratum granulosum down to the lowest abnormal cell
- Prognosis is based on the depth of dermal invasion (Breslow depth) for local melanoma
