Two pathways of generating monoclonal gammopathy of undetermined significance (MGUS)/multiple myeloma (MM) tumors.

Tumors can be generated either with (+) or without (−) the occurrence of a primary translocation, the former being mainly nonhyperdiploid and the latter mainly hyperdiploid. Dysregulation of a cyclin D gene appears to be an early event in each case. Secondary translocations can occur in both kinds of tumors. As indicated, tumors in the former pathway selectively generate stromal independent MM cell lines, but the dashed arrows suggest the possibility that the latter pathway might generate cell lines.