Criteria
Histological features
Diagnosis of melanoma is made following histological analysis of tissue; usually skin but in some cases from lymph nodes and other organ tissues.
Key histological characteristics of melanoma include:[78]
Severe atypical melanocytes
Architectural disorder characterised by asymmetrical growth pattern within the epidermis
Pagetoid scatter of melanocytes above the basal cell layer of the epidermis, confluent growth with a loss of the normal nested growth pattern of junctional melanocytes
Absence of maturation of the dermal melanocytic component with depth in the dermis.
Other abnormal features include regression (seen as dermal fibrosis with pigmented melanophages) and mitotic figures in the dermal melanocytic component.[78]
Prognostic information is also provided with a skin biopsy of a melanoma, including tumour thickness measured as Breslow's thickness (depth of invasion measured in millimetres from the top of the granular cell layer to the point of deepest tumour penetration in the dermis or subcutis), ulceration, mitotic count, vascular invasion, and microscopic satellites.[14][63]
Breslow's thickness
Depth of invasion (measured with a micrometre on a microscope during histopathological evaluation of a biopsy specimen) in millimetres from the top of the granular cell layer to the point of deepest tumour penetration in the dermis or subcutis:[63]
Thin: <1 mm
Intermediate thickness: 1 mm to 4 mm
Thick: >4 mm.
Melanoma confined to the epidermis is termed melanoma-in-situ.
Clark's level
Clark's level is a measure of tumour thickness, but is less accurate than Breslow's thickness. Use of the Clark's level is primarily restricted to assessment of tumours <1 mm thickness. Clark's level is determined by the level of invasion of malignant cells in the dermis or subcutis, with:[79]
Level I corresponding to in-situ melanoma [Figure caption and citation for the preceding image starts]: Photomicrograph of melanoma in situFrom the personal collection of Dr Hobart Walling and Dr Brian Swick. [Citation ends].
Level II corresponding to invasion within the papillary dermis
Level III corresponding to invasion filling the papillary dermis
Level IV corresponding to invasion within the reticular dermis [Figure caption and citation for the preceding image starts]: Photomicrograph of Clark's level IV invasive melanomaFrom the personal collection of Dr Hobart Walling and Dr Brian Swick. [Citation ends].
Level V corresponding to invasion into the subcutis.
Clinical staging of melanoma: American Joint Committee on Cancer TNM staging system (8th Edition)[62]
The American Joint Committee on Cancer (AJCC) staging system describes the extent of disease based on the following anatomic factors: size and extent of the primary tumour (T); regional lymph node involvement (N); and presence or absence of distant metastases (M). Non-anatomic prognostic factors (e.g., tumour grade, biomarkers) may be used to supplement the staging of certain cancers.
In general, cutaneous melanoma is categorised as:[14]
Localised disease (no evidence of metastases, stage I-II)
Regional disease (stage III)
Distant metastatic disease (stage IV).
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