Pre- and postgain deletions in MM. Deletions preceding chromosomal gains were detected in 9.4% of hyperdiploid MMs (top), a quarter of which affected TSGs or oncogenes and likely represented the initiating events. Deletions acquired after large chromosomal gains are even more common, found in one-third of patients with MM (either hyperdiploid or bearing IGH translocations). These secondary driver events promote disease progression and are associated with dismal prognosis.