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Clark's index (level of invasion of malignant melanoma)

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According to Clark (1), there are five levels of invasion for malignant melanoma which are another factor used in assessing prognosis:

I: confined to epidermis, in situ

II: invasion of the papillary dermis

III: filling of the papillary dermis, but no extension into the reticular dermis

IV: invasion of the reticular dermis

V: invasion of the subcutaneous tissue

However, the usage of Clark levels has now been replaced by the updated melanoma staging system which uses more reliably predictive features such as ulceration, mitotic count and Breslow depth.

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)
  • presence or absence of distant metastases (M). (2)

Non-anatomic prognostic factors (e.g., tumour grade, biomarkers) may also be used to supplement the staging of certain cancers.

In general, cutaneous melanoma is categorised as:(3)

  • Localised disease (no evidence of metastases, stage I-II)
  • Regional disease (stage III)
  • Distant metastatic disease (stage IV).

Reference:

  1. Clark, W.H., Jr.: A classification of malignant melanoma in man correlated with histogenesis and biologic behaviour. In Montagna W, Hu F (eds): Advances in Biology and Skin, Vol 8, The Pigmentary System, Pergamon Press, New York, 1966: 612-647.
  2. Amin MB, Edge S, Greene F, et al, eds. AJCC cancer staging manual. 8th ed. New York, NY: Springer; 2017.
  3. National Comprehensive Cancer Network. NCCN clinical practice guidelines in oncology: melanoma - cutaneous [internet publication].

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