Plasma cell labeling index and β₂-microglobulin predict survival independent of thymidine kinase and C-reactive protein in multiple myeloma

The plasma cell labeling index (PCLI) and serum β₂-micro-globulin (β₂M) are independent prognostic factors in multiple myeloma (MM). Recently, levels of thymidine kinase (TK) and C-reactive protein (CRP) have been shown to have prognostic value. We studied 107 patients with newly diagnosed myeloma to determine whether TK and CRP values added prognostic information not already available using the PCLI and β₂M. Univariate survival analysis showed prognostic significance for the PCLI, TK, β₂M, age, serum albumin, and CRP. Multivariate analysis showed that only PCLI and β₂M have independent prognostic significance. The survival curves were better separated using the PCLI and β₂M than with other combinations of variables. Among nine patients under age 65 with low PCLI and low β₂M, eight were alive almost 6 years after starting chemotherapy. These good-risk patients could not be identified by standard clinical features. Although creatinine and calcium were normal, other features such as bone lesions, osteoporosis, fracture, and anemia were present and stage distribution was similar to other patients in the study. In conclusion, PCLI and β₂M measured at diagnosis are independent prognostic factors. They must be considered when interpreting the results of clinical trials and should be helpful in counseling patients and in designing new trials. When the PCLI and β₂M values are known, the TK and CRP values do not add useful additional prognostic information.