[In vitro chemosensitivity assay using a double-layer-agar system: human tumor cloning assay and thymidine...

Human tumor cloning assay (HTCA) and thymidine incorporation assay (TIA) were both performed using a double-layer-agar system with continuous exposure of cells to standard anticancer drugs. The rate of evaluable assays was 44% (280 of 638 tumor samples) in HTCA and 48% (216 of 452) in TIA. When the tumor samples were restricted to the gastric and colorectal cancers, it was significantly higher in TIA than HTCA (p < 0.01). HTCA was 95% reliable for predicting in vivo resistance and 52% reliable for in vivo sensitivity, whereas TIA was 88% reliable for in vivo resistance and 44% for in vivo sensitivity. These results seem to suggest that it is unnecessary to select just clonogenic tumor cells among whole tumor cell population in assessing chemosensitivity of human tumors. The current study also indicates that chemotherapy with in vitro sensitive drugs assessed by TIA produced longer survival of the patients with stage III or IV gastric cancer. Most of clinical correlation trials including this study, however, have been performed retrospectively. The prospective study is necessary to determine whether drug selection by in vitro assays is superior to that by an experienced oncologist. In addition, further studies on pharmacokinetics of anticancer drugs are required to solve some other problems inherent to the current chemosensitivity assays.