The use of [3H]thymidine incorporation assay (TIA) to evaluate the drug response of tumor cells has been recognized as a useful chemosensitivity assay for fresh human tumor specimens. However, its low evaluability has been a disadvantage for clinical application. To overcome this drawback, we have applied a preculture stage prior to the TIA. This preculture requires plating the tumor cell suspension onto a collagen matrix for 24 h. In 29 fresh human tumor specimens, a significant increase in both cell viability (P < 0.05) and [3H]thymidine incorporation (P < 0.001) of the cultured cells was observed with preculturing; the composition of cancer cells (epithelial membrane antigen positive) and stromal cells (vimentin positive) did not change. In comparisons between 66 specimens that were precultured and 705 specimens that were not, the evaluability rate increased significantly from 48.5% (342/705) to 75.8% (50/66; P < 0.0001) after preculturing. No significant change in in vitro chemosensitivities was observed. When the clinical responses for cancer chemotherapy were retrospectively compared with the in vitro sensitivities of the corresponding drugs on 16 patients who had measurable lesions, the correlation between the two was satisfactorily strong; the prediction accuracy for sensitivity was 83.3% (5/6), the prediction accuracy for resistance was 95.0% (19/20), and the overall correlation was 92.3% (24/26). These results indicate that TIA with preculturing yields increased rates of evaluability, preserving in vitro drug responses of cultured tumor cells, and has an improved potential to be used for determining clinical chemotherapy.

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