Rapid Response to Treatment of Multiple Myeloma Detected with FDG PET Scanning in Multiple Myeloma - Early Results from Total Therapy III.

Fluorodeoxyglucose Positron Emission Tomography (PET) scanning can rapidly detect and quantify changes in tumor metabolism. We present early results from the first 47 patients enrolled in Total Therapy III for multiple myeloma using PET scanning and correlating with serum M protein. Since we have previously demonstrated that diffuse uptake patterns do not have prognostic significance, we have limited our assessment of these 47 patients to those with one or more PET-defined focal lesions (FL) at baseline who have had at least one follow-up PET scan (25 patients). Of this group of 25, 10 have had a second follow-up scan. These whole body PET scans were performed at baseline and at time points corresponding to immediately after two cycles of VDT-PACE, landmarks LMK1 and LMK2. Patients with complete resolution of FL on PET are considered to be in PET-CR. We find that 17/25 (68%) had a decrease in number of FL from baseline to LMK1 and 8/10 (80%) had a decrease in number of FL from baseline to LMK2. In addition, 6/25 (24%) were in PET-CR by LMK1 and 3/10 (30%) in PET-CR by LMK2. Similarly, a decrease in serum M-protein was seen in 16/25 (64%) from baseline to LMK1 and in 8/10 (80%) from baseline to LMK2.

At baseline, 10 patients had serum M protein levels of 0.01 g/dl or less. Of these, 8 (80%) had PET-defined focal lesions, demonstrating PET’s ability to monitor tumor metabolism in the face of hypo- or non-secretory disease. Of these, 7 have been enrolled sufficient time to have a second PET scan, with 6/7 (86%) demonstrating a continuing decrease in number of FL in response to treatment. At baseline, PET detected 5 of 47 patients with extramedullary disease (EMD), a finding of severe adverse prognostic significance at baseline. Of these patients, all had FL at baseline PET and all had decreasing number of FL on first follow-up PET scan (two have had a second follow-up scan, one improving and one PET-CR). One of these patients with EMD is nonsecretory.

From these data, we conclude that functional imaging with PET scanning offers important and unique information about early tumor response that improves patient management by demonstrating rapid change in response to treatment that not only parallels serum M-protein response but which also is reliable in hypo- or non-secretory disease as well as in detection and monitoring of extramedullary tumor, an ominous condition that is particularly difficult to detect in the hypo- or non-secretory patient.