Venn diagram showing approximate 5-yr metastasis-free survival rates in the 8 combinations of depth, size and grade (high=III-IV). For exact survival rates see Table 4. Green fields include the four subsets of low grade tumors. The survival rates are between 1 and 0.9 irrespective of depth and size. Blue fields include the two subsets of small high grade tumors, both with survival rates of 0.8. Red fields include the two subsets of large and high grade tumors. The survival rates differ, being 0.7 for superficial tumors and 0,5 for deep tumors. The explanation is that the mean size of deep-seated, large tumors is greater than that of superficial, large tumors, see Table 2. The principal findings are the same when high grade is defined as grade IV, see Table 5.