Clark's level is a staging system, used in conjunction with Breslow's depth, which describes the level of anatomical invasion of the melanoma in the skin. It was developed by Wallace H. Clark Jr. at Harvard University and Massachusetts General Hospital in the 1960s.
Five anatomical levels are recognized, and higher levels have worsening prognostic implications. These levels are:
- Level 1: Melanoma confined to the epidermis (melanoma in situ)
- Level 2: Invasion into the papillary dermis
- Level 3: Invasion to the junction of the papillary and reticular dermis
- Level 4: Invasion into the reticular dermis
- Level 5: Invasion into the subcutaneous fat.
Clark's level was the primary factor in earlier AJCC staging schemae for melanoma. However, with further study, it has been shown that Clark's level has a lower predictive value, is less reproducible, and is more operator-dependent as compared with Breslow's depth. Thus, in the current (as of 2010) AJCC staging system, Clark's level has prognostic significance only in patients with thin (Breslow depth <1 mm) melanomas.
- Balch, CM; Soong, SJ; Gershenwald, JE; Thompson, JF; Reintgen, DS; Cascinelli, N; Urist, M; McMasters, KM; et al. (2001). "Prognostic factors analysis of 17,600 melanoma patients: Validation of the American Joint Committee on Cancer melanoma staging system". Journal of Clinical Oncology. 19 (16): 3622–34. PMID 11504744.