Endocrine therapy testing of human breast cancers in the soft agar clonogenic assay

The human tumor soft agar cloning assay has been used to assess the biological effects of cytotoxic drugs and other agents on human cancers. In this study we have examined the effects of two hormonal agents, tamoxifen (Tam) and medroxyprogesterone acetate (MPA), on colony growth of the MCF-7 human breast cancer cell line as well as fresh human breast cancer specimens. Using standard criteria for a colony (greater than 50 cells or greater than 60 microns in diameter) Tam (1.0 microM) reduced MCF-7 colony formation by only 30% to 50%, and MAP (1.0 microM) had no effect. However, both agents dramatically reduced the formation of larger colonies; less than 10% of colonies larger than 124 microns survived Tam exposure, and less than 25% survived with MPA. In vitro sensitivity (less than 30% colony survival) of fresh human breast cancer specimens was observed infrequently with either Tam (1/39 evaluable assays) or MPA (3/36 evaluable assays). Colony growth of human breast cancer was unaltered when cells were plated in charcoal-stripped serum to reduce the endogenous estrogen concentration. In vitro sensitivity to Tam or MPA was not increased under these conditions. No correlation was found between estrogen receptor (ER) concentration and inhibition of colony survival with Tam or MPA. None of 16 assays from ER-positive specimens treated with Tam and 2 of 18 ER-positive specimens treated with MPA were sensitive in vitro. In contrast, 2 of 12 ER-negative specimens tested with Tam and 3 of 7 ER-negative specimens tested with MPA were sensitive in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)