Identification of BAC clones by a decision-tree algorithm to classify the gastric cancers into two groups with different characters. (a) Differentiation between gastric cancers with and without node metastasis. These two groups can be clearly differentiated by examining the degree of the copy number changes of six BAC clones mapped to 5q13.2, 13q31.1, 1p22.3, 1p34.2, 14q32.2, and 3q13.12 in descending order. A tumor of which the copy number at 5q13.2 was ≤ -0.346 (log2) shows no node metastasis. When the DNA copy number of the tumor was not the case at the first clone, the second criterion (>-0.37 at 13q31.1) was checked. Five tumors were separated from the remaining 77 tumors at this point. When the DNA copy number of the clone at 13q31.1 was ≦ 0.37 in the tumor, the third clone located on 1p22.3 was examined. If the DNA copy number of the tumor meets the criterion of the third clone, ≦ -0.042, nodal metastasis was positive in this tumor. Thirty-six cancers were classified into this category at this point. In this way, the DNA copy number of the tumor was in turn examined from the first to the sixth clone. Each step successively sorts a cluster of either group. Eventually, all gastric cancers were classified into either of two groups, cancers with and without node metastasis. The figures in parentheses indicate the number of tumors fitting the requirements. The correctly classified instances were 83 (100%), and the incorrectly classified instances were 0 (0%). In this classifier, the number of leaves is seven, and the size of the tree was 13. In the same way as the case of node metastasis, BAC clones and their copy numbers were determined for liver metastasis (b), peritoneal dissemination (c), depth of tumor invasion (early or advanced cancer)(d), and histologic type (e).