KINETICS OF PRIMARY TUMOR-REGRESSION WITH CHEMOTHERAPY - IMPLICATIONSFOR THE TIMING OF SURGERY

Purpose: The kinetics of tumor regression during administration of che motherapy has relevance to the timing of surgery. The aim of this stud y was characterization of the time course of primary tumor regression in initially unresectable rhabdomyosarcoma, hepatoblastoma, and neurob lastoma patients. We also estimated the total cell number in the prima ry tumor at diagnosis. Methods: Tumor volumes of 24 pediatric patients with either unresectable rhabdomyosarcoma, hepatoblastoma, or neurobl astoma were determined by using computerized three-dimensional reconst ruction from serial computed tomography (CT) scans during chemotherapy . Cell densities were calculated by counting cell numbers in high-powe r fields and dividing by area and section thickness, Cell number at di agnosis was then calculated. Results: Median tumor volumes at diagnosi s were 175 cc, 748 cc, and 738 cc for rhabdomyosarcoma, neuroblastoma, and hepatoblastoma, respectively. The median tumor cell counts were 3 1, 68, and 59x10(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 tum or volume with chemotherapy was observed in rhabdomyosarcoma, neurobla stoma, and hepatoblastoma. These data suggest that second-look resecti on may be feasible after two to three cycles of chemotherapy. This hyp othesis may be tested by randomizing the timing of second-look surgica l intervention.