Purpose: The kinetics of tumor regression during administration of chemotherapy has relevance to the timing of surgery. The aim of this study was characterization of the time course of primary tumor regression in initially unresectable rhabdomyosarcoma, hepatoblastoma, and neuroblastoma patients. We also estimated the total cell number in the primary tumor at diagnosis.
Methods: Tumor volumes of 24 pediatric patients with either unresectable rhabdomyosarcoma, hepatoblastoma, or neuroblastoma were determined by using computerized three-dimensional reconstruction from serial computed tomography (CT) scans during chemotherapy. Cell densities were calculated by counting cell numbers in high-power fields and dividing by area and section thickness. Cell number at diagnosis was then calculated.
Results: Median tumor volumes at diagnosis were 175 cc, 748 cc, and 738 cc for rhabdomyosarcoma, neuroblastoma, and hepatoblastoma, respectively. The median tumor cell counts were 31, 68, and 59 x 10(10) cells/tumor for rhabdomyosarcoma, neuroblastoma, and hepatoblastoma, respectively. The tumor regression was most rapid during the first two cycles, and little change in volume was observed after three cycles.
Conclusion: Rapid initial reduction in primary tumor volume with chemotherapy was observed in rhabdomyosarcoma, neuroblastoma, and hepatoblastoma. These data suggest that second-look resection may be feasible after two to three cycles of chemotherapy. This hypothesis may be tested by randomizing the timing of second-look surgical intervention.