Hormone dependency of human breast neoplasma cultured in vitro in the stem cell assay

The stem cell soft agar culture system provides a biological tool with which to study tumor clones derived from heterogeneous tumor cell populations. For testing the feasibility of this approach in indentifying hormone-responsive clones of mammary tumors, a study was done to determine whether estrogen deprivation or supplementation would alter colony formation in sequential breast neoplasms received in the Cell Kinetics Laboratory, The Pennsylvania State University. Single-cell suspensions obtained from 22 freshly excised breast neoplasms (20 malignant, 2 benign) were plated in soft agar with and without tamoxifen (Tam) (10^-7 M) with the use of serum-supplemented media and with and without 17β-estradiol (E₂) (10^-8 M) under serum-free medium conditions. Twenty tumors successfully grew, producing 42 ± 8 (mean ± SEM) colonies in control dishes in the presence of serum and 27 ± 5 in its absence (P < .001). Tam inhibited colony formation in 78% of malignant tumors, whereas a stimulatory effect was observed with E₂ in 94%. An increase in colony formation was induced by Tam in 4 tumors (2 benign and 2 malignant). The effects of E₂ and Tam on tumor growth were not influenced by the estrogen and prosgesterone receptor status of the tumor. These preliminary results suggest that all tumors, irrespective of their receptor status, may contain clones of hormone-responsive cells.