Deletion of chromosome 13 detected by conventional cytogenetics is a critical prognostic factor in myeloma

In myeloma, the prognostic impact of different strategies used to detect chromosome 13 deletion (Δ13) remains controversial. To address this, we compared conventional cytogenetics and interphase fluorescence in situ hybridization (iFISH) in a large multicenter study ( n =794). The ability to obtain abnormal metaphases was associated with a poor prognosis, which was worse if Δ13, p53 deletion or t(4;14) was present, but only Δ13 remained significant on multivariate analysis. Patients with Δ13, by either cytogenetics or iFISH, had a poor prognosis. However, when cases with Δ13 detectable by both cytogenetics and iFISH were separated from those detected by iFISH only, the poor prognosis of iFISH-detectable Δ13 disappeared; their outcome matched that of patients with no detectable Δ13 ( P =0.115). Addition of ploidy status to iFISH-Δ13 did not affect the prognostic value of the test. Indeed both cytogenetics and iFISH Δ13 divided both hyperdiploidy and nonhyperdiploidy into two groups with similar prognoses, indicating that the poor prognosis of ploidy is entirely due to its association with Δ13. We conclude that Δ13 detected by metaphase analysis is a critical prognostic factor in myeloma. Absence of Δ13, even in those patients yielding only normal or no metaphases, is associated with a relatively good prognosis.