More recently there has been some suggestion that CDKN2B may also have tumor suppressor functions in melanoma. Krimpenfort et al. (2007) showed that mice null for CDKN2B, CDKN2A, and P14ARF were more tumor prone than CDKN2A/P14ARF null mice and developed a predominance of skin tumors (Krimpenfort et al.,2007). The authors suggested that CDKN2B might act as critical “back up” tumor suppressor in cells null for CDKN2A.