Prognostic value of the serum free light chain ratio in newly diagnosed myeloma: proposed incorporation into the international staging system

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Abstract
To determine if the serum free light chain (FLC) ratio has prognostic value in patients with symptomatic multiple myeloma (MM), baseline serum samples from a well-characterized cohort of 790 newly diagnosed MM patients were tested with the FLC assay. FLC ratio was calculated as κ/λ (reference range 0.26–1.65). On the basis of the distribution of values, a cutpoint κ/λ FLC ratio of 32 was chosen for further analysis. Overall survival was significantly inferior in patients with an abnormal FLC ratio of 32 (n=479) compared with those with an FLC ratio between 0.03 and 32 (n=311), with median survival of 30 versus 39 months, respectively. We incorporated abnormal FLC ratio with the International Staging System (ISS) risk factors (that is, albumin 2-microglobulin ⩾3.5 g/l), to create a risk stratification model with improved prognostic capabilities. Patients with 0, 1, 2 or 3 adverse risk factors had significantly different overall survival, with median survival times of 51, 39, 30 and 22 months, respectively (P<0.001). These findings suggest that the serum FLC ratio at initial diagnosis is an important predictor of prognosis in myeloma, and can be incorporated into the ISS for improved risk stratification.