Identification of a tumor-related subclone in the blood and BM of patient 10. Cloning of individual V_L -genes revealed that a tumor-related subclone (clone 2) formed a minor (5 of 25) and a dominant (21 of 30) subset of sequences isolated from the blood and BM of patient 10, respectively. The subclone was not detected in the primary tumor (n = 25). The primary tumor sequence (clone 1) identified from the cerebral site differed from the subclone by the acquisition of 6 mutations, of which 5 were replacement mutations (amino acid [aa] positions 10, 19, and 27-29) and 1 was a silent mutation (aa position 7). The subclone also featured 3 silent mutations (aa positions 22, 77, and 89) that were not observed in the tumor clone. The specificity of the primer ensured a clonal relationship of the subclone, and this was strengthened by the presence of intraclonal variant base changes shared between the primary tumor sequence and the subclone in both blood and BM at aa positions 7, 10, 51, 77, and 89. The tissue type and the observed frequency of the sequence are indicated on the left. The unique complementarity determining region-3 sequence to which the specific primer was designed to anneal is underlined. Dots represent identity to germline. Mutations at the aa level are shown as uppercase letters for replacement mutations or as lowercase letters for silent mutations.