Immunoglobulin synthesis and total body tumor cell number in IgG multiple myeloma.

Studies of synthesis of IgG paraproteins were performed in 10 patients who had IgG myeloma in order to quantitate cellular immunosynthetic functions and derive estimates of the number of tumor cells present in such patients. Serial in vitro studies demonstrated constancy in the cellular rate of IgG paraprotein secretion for up to 8 months. Average molecular synthesis rates in different patients ranged from 12,500 to 85,000 molecules of IgG per minute per myeloma cell. Estimated total body tumor cell number ranged from 0.5 x 10(12) to 3.1 x 10(12) myeloma cells, and could be correlated with the degree of skeletal damage observed on roentgenograms (P = <0.01). Serial measurements of tumor cell number may prove useful in characterizing the growth rate and natural history of multiple myeloma. Myeloma is the first metastatic human malignancy in which quantitative measurements of the body's burden of malignant cells have been obtained.