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:
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 (2010) AJCC staging system, Clark's level has prognostic significance only in patients with thin (Breslow depth <1 mm) melanomas.