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. 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.