A melanoma, frequently called a malignant melanoma, is an aggressively malignant cancer that develops in epithelial cells capable of producing melanin. It appears most often on the skin, but, also, in the eye, or, rarely, in the mucous membranes of the genitalia, anus, oral cavity, or other sites. Early detection is critical, as localized melanoma usually can be surgically excised, but metastatic disease has a poor prognosis.
It occurs mostly in adults and may originate de novo or from a pigmented nevus or malignant lentigo. Melanomas frequently metastasize widely, and the regional lymph nodes, liver, lungs, and brain are likely to be involved. The incidence of malignant skin melanomas is rising rapidly in all parts of the world.
The microstage of malignant melanoma is determined on histologic examination by the anatomic level of local invasion (Clark classification) and/or the vertical thickness of the lesion in millimeters (Breslow classification). Accurate microstaging of the primary tumor requires careful histologic evaluation of the entire specimen by an experienced pathologist. Estimates of prognosis should be modified by sex and anatomic site as well as by clinical and histologic evaluation.
The Clark Classification is qualitative.
- Level I: Lesions involving only the epidermis (in situ melanoma); not an invasive lesion.
- Level II: Invasion of the papillary dermis but does not reach the papillary-reticular dermal interface.
- Level III: Invasion fills and expands the papillary dermis but does not penetrate the reticular dermis.
- Level IV: Invasion into the reticular dermis but not into the subcutaneous tissue.
- Level V: Invasion through the reticular dermis into the subcutaneous tissue.
If the lesion is greater than 1.5mm thick, the Breslow thickness measurement is more reproducible and a better predictor of progress than the Clark classification.
The American Joint Committee on Cancer (AJCC) has designated staging by TNM classification to define melanoma.
Primary tumor (T)
- TX: Primary tumor cannot be assessed (e.g., shave biopsy or regressed melanoma)
- T0: No evidence of primary tumor
- Tis: Melanoma in situ
- T1: Tumor 1.0 mm or less in thickness with or without ulceration
- T1a: Tumor 1.0 mm or less in thickness and Clark level II or III with no ulceration
- T1b: Tumor 1.0 mm or less in thickness and Clark level IV or V or with ulceration
- T2: Tumor more than 1.0 mm but 2.0 mm or less in thickness with or without ulceration
- T2a: Tumor more than 1.0 mm but 2.0 mm or less in thickness with no ulceration
- T2b: Tumor more than 1.0 mm but 2.0 mm or less in thickness with ulceration
- T3: Tumor more than 2.0 mm but 4.0 mm or less in thickness with or without ulceration
- T3a: Tumor more than 2.0 mm but 4.0 mm or less in thickness without ulceration
- T3b: Tumor more than 2.0 mm but 4.0 mm or less in thickness with ulceration
- T4: Tumor more than 4.0 mm in thickness with or without ulceration
- T4a: Tumor more than 4.0 mm in thickness without ulceration
- T4b: Tumor more than 4.0 mm in thickness with ulceration
Regional lymph nodes (N)
[Note: Micrometastases are diagnosed after elective or sentinel lymphadenectomy; macrometastases are defined as clinically detectable lymph nodes metastases confirmed by therapeutic lymphadenectomy, or when any lymph node metastasis exhibits gross extracapsular extension.]
- NX: Regional lymph nodes cannot be assessed
- N0: No regional lymph node metastasis
- N1: Metastasis to one lymph node
- N1a: Clinically occult (microscopic) metastasis
- N1b: Clinically apparent (macroscopic) metastasis
- N2: Metastasis to two or three regional nodes or intralymphatic regional metastasis without nodal metastases
- N2a: Clinically occult (microscopic) metastasis
- N2b: Clinically apparent (macroscopic) metastasis
- N2c: Satellite or in-transit metastasis without nodal metastasis
- N3: Metastasis in more than four regional nodes, or matted lymph nodes, or in-transit metastasis or satellite(s) with metastatic regional node(s)
Distant Metastasis (M)
- MX: Distant metastasis cannot be assessed
- M0: No distant metastasis
- M1: Distant metastasis
- M1a: Metastasis to skin, subcutaneous tissues, or distant lymph nodes
- M1b: Metastasis to lung
- M1c: Metastasis to all other visceral sites or distant metastasis at any site associated with an elevated serum lactic dehydrogenase
Treatment and prognosis