Cytogenetic abnormalities correlate with the plasma cell labeling index and extent of bone marrow involvement in myeloma.

Chromosomal abnormalities have biologic and prognostic significance in multiple myeloma, especially among patients with relapsed disease. We report the relationship between chromosomal abnormalities and known prognostic factors such as plasma cell labeling index (PCLI) and bone marrow plasma cell involvement in 75 consecutive patients undergoing autologous stem cell transplantation for relapsed or refractory myeloma. Thirty of 70 patients (43%) had a chromosomally abnormal clone in their bone marrow, and in most cases the karyotype was complex (> 3 abnormalities). Patients with an abnormal clone on cytogenetic analysis had a higher PCLI (median, 1.4) than patients with a normal karyotype (0.2) (P < 0.001). Bone marrow plasma cell percentage also differed: median 48% versus 20%, respectively (P < 0.001). The PCLI and bone marrow plasma cell percentage correlated positively with the percentage of abnormal metaphases on conventional cytogenetic analysis: rho 0.60 (P < 0.001) and 0.46 (P < 0.001), respectively. We categorized patients into those with 20% or more abnormal metaphases, less than 20% abnormal metaphases, and only normal metaphases. The median PCLI values were 3.3, 1.1, and 0.3, respectively (P < 0.001). The bone marrow plasma cell percentage median values were 62%, 40%, and 25%, respectively (P = 0.003). Chromosomal abnormalities may offer a proliferative advantage to the neoplastic plasma cell, thereby leading to an unfavorable outcome.