Variations in exposure to mitomycin C in an in vitro colony-forming assay

The effect of mitomycin C on two human ovarian cancer cell lines was measured during several exposure times and concentrations using the Human Tumour Colony-forming Assay (HTCA). Changes in exposure time and concentration resulted in considerable differences in tumour cell survival. It is concluded that several exposure times and concentrations are necessary for in vitro sensitivity testing. We suggest alternative criteria derived from pharmacokinetic data in patients instead of one-tenth of the peak plasma level which is the usual practice.