In vitro soft agar assay by use of multiple for screening of tumor sensitivity to anticancer drugs.

For use in routine clinical studies, modifications in Hamburger's stem cell assay were made. A multiple with 24 wells made feasible, handling of a large number of samples. The addition of anticancer drugs to the bottom layer of agar led to avoidance of exposure to drugs before cell plating and evaluation of the effect of long-acting drugs such as 5-fluorouracil. Storage of the test plate including anticancer drugs in a freezer at -70 degrees C showed no loss of the colony forming activity. This method is simple, reliable and readily facilitated.