The plasma cell labeling index: a valuable tool in primary systemic amyloidosis

The plasma cell labeling index (LI) is of value in predicting prognosis in multiple myeloma. Primary systemic amyloidosis (AL) is a plasma cell dyscrasia that shares many features with myeloma. We obtained bromodeoxyuridine LI on 125 patients who presented with AL, 22 of whom also had overt multiple myeloma. Forty-six patients had a plasma cell LI greater than 0%. Of the 46 patients with an elevated LI, 19 (41%) had multiple myeloma as compared with three (4%) of the 79 patients with an LI = 0 (P less than .0001). A response to chemotherapy was seen in 14 (30%) of 46 patients with an LI greater than 0, as compared with ten (13%) of 79 patients with an LI of 0 (P = .015). The median survival of the high LI group was 14.6 months v 29.8 months for the low LI group (P = .02). In the low LI group, 29% are projected to be alive at 60 months, as compared with 20% in the high LI group. When patients with myeloma were excluded from the analysis, the LI did not predict response but continued to indicate a survival disadvantage (P less than .05). The major utility of the LI was in identifying those patients most likely to have multiple myeloma and those AL patients with a poor prognosis (median survival, 14.1 months).