Contribution of prednisone to the effectiveness of hexamethylmelamine in multiple myeloma.
The Eastern Cooperative Oncology Group evaluated hexamethylmelamine in 89 patients with advanced refractory or relapsing multiple myeloma. Hexamethylmelamine was initially used as a single agent administered orally at 200 mg/m2/day for the first 3 weeks of each 4-week cycle. When this regimen proved to be ineffective, it was modified first by increasing the dose of hexamethylmelamine to 280 mg/m2/day and subsequently by adding prednisone at 75 mg for the first 7 days of each 28-day cycle. None of the 39 patients receiving hexamethylmelamine without prednisone had an objective response, while two patients had minimal objective improvement (25%-50% decrease in M protein with symptomatic improvement). Only 14% of these patients had objective or symptomatic response or both. In contrast, patients treated with hexamethylmelamine plus prednisone had a 22% objective response rate, with another 14% showing lesser degrees of objective improvement. Fifty-one percent of the patients treated with this regimen had either objective or symptomatic improvement or both. Severe (grade 3) toxicity was seen in nearly two-thirds of the patients on the higher-dose hexamethylmelamine regimens compared with 37% of the patients receiving low-dose hexamethylmelamine; however, in most instances this represented rapidly reversible cytopenias. Because all but one of the patients responding to hexamethylmelamine plus prednisone had experienced previous treatment failure on regimens containing prednisone in similar dose and schedules, it is unlikely that the responses are due to prednisone alone. Instead, this study suggests that the activity of hexamethylmelamine in multiple myeloma is dependent on the concomitant administration of prednisone and that the combination regimen appears to be synergistic.