Hyperdiploidy is a common finding in monoclonal gammopathy of undetermined significance and monosomy 13 is restricted to these hyperdiploid patients.

Purpose: Two pathways, hyperdiploid and nonhyperdiploid, are proposed for progression to plasma cell neoplasia. Implication of monosomy 13 (Delta13) is unclear in monoclonal gammopathy of undetermined significance (MGUS), and data on DNA content of plasma cells [DNA index (DI)] are rare.

Experimental Design: We ascertained DI in 169 multiple myeloma (MM) and 96 MGUS patients.