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 (Delta 13) 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 Delta 13, p53 deletion or t(4; 14) was present, but only Delta 13 remained significant on multivariate analysis. Patients with Delta 13, by either cytogenetics or iFISH, had a poor prognosis. However, when cases with Delta 13 detectable by both cytogenetics and iFISH were separated from those detected by iFISH only, the poor prognosis of iFISH-detectable Delta 13 disappeared; their outcome matched that of patients with no detectable Delta 13 (P = 0.115). Addition of ploidy status to iFISH-Delta 13 did not affect the prognostic value of the test. Indeed both cytogenetics and iFISH Delta 13 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 Delta 13. We conclude that Delta 13 detected by metaphase analysis is a critical prognostic factor in myeloma. Absence of Delta 13, even in those patients yielding only normal or no metaphases, is associated with a relatively good prognosis.