Effects of estrogens and antiestrogens on cell proliferation: implications for the treatment of breast cancer

A randomized placebo-controlled study of tamoxifen after adjuvant chemotherapy in premenopausal women with early breast cancer (National Cancer Institute of Canada--Clinical Trials Group Trial, MA.12)

BACKGROUND

In the early 1990s, the role of adjuvant tamoxifen in premenopausal women with early breast cancer (EBC) was not established. Similarly, optimum timing relative to adjuvant chemotherapy and efficacy of tamoxifen in hormone receptor-negative tumors were unclear.

PATIENTS AND METHODS

Premenopausal women with EBC, any hormone receptor status, after surgery received standard adjuvant chemotherapy [doxorubicin (adriamycin)/cyclophosphamide, cyclophosphamide/methotrexate/5-fluorouracil, or cyclophosphamide/epirubicin/5-fluorouracil] followed by randomization to tamoxifen or placebo for 5 years. Outcomes were overall survival (OS), disease-free survival (DFS), toxicity, and compliance with therapy.

RESULTS

Median follow-up for 672 women was 9.7 years. Multivariate analysis showed improved DFS [78.2% versus 71.3% at 5 years; hazard ratio (HR) 0.77; P = 0.056] and a trend for improved OS (86.6% versus 82.1% at 5 years; HR 0.78; P = 0.12). There was no evidence of greater benefit for the receptor-positive subgroup. Compliance with treatment was suboptimal in both arms, with 103 (31%) women on tamoxifen and 70 (21%) on placebo-stopping therapy early because of toxicity, refusal, or other choices.

CONCLUSIONS

Adjuvant tamoxifen, given after chemotherapy to premenopausal women with EBC, improved 5-year DFS. Poor compliance may have reduced treatment efficacy.

The best use of adjuvant endocrine treatments

Endocrine therapy remains important in the adjuvant treatment of pre- and postmenopausal women. Adjuvant ovarian ablation with or without tamoxifen produces effects which are equivalent to those of CMF (cyclophosphamide, methotrexate and 5-fluorouracil) chemotherapy in premenopausal women with oestrogen receptor (ER) and/or progesterone receptor (PgR) positive breast cancer. Tamoxifen alone is also effective in these women. Concurrent use of tamoxifen and ovarian ablation may be even more effective, but more studies are needed. Tamoxifen remains a standard adjuvant therapy for postmenopausal women with ER and/or PgR positive tumours. Current information supports the use of 5 years of tamoxifen but additional studies comparing 5 years to longer duration are ongoing. The aromatase inhibitor (AI) anastrozole has now been demonstrated to be better than tamoxifen in preventing recurrence in early reports from the Arimidex vs Tamoxifen And the Combination (ATAC) Trial. Ongoing trials of this and other AIs before, after, concurrent with, or substituted for tamoxifen in the adjuvant setting may soon revolutionize our approach for postmenopausal women. Adjuvant bisphosphonates have been shown to reduce the incidence of bone metastases and improve survival in two of three published adjuvant trials and are being further studied. Her-2 neu status is being explored as a predictive factor for selection of endocrine therapy, but is not yet considered standard for this purpose.

DDT stimulates c-erbB2, c-met, and STATS tyrosine phosphorylation, Grb2-Sos association, MAPK phosphorylation, and proliferation of human breast epithelial cells

Several environmental organochlorines, some of which exhibit estrogenic activity, have been detected in human breast tissue and have been suggested as having a role in tumorigenesis. In this communication, we report the effects of DDT on c-erbB2 and c-met growth factor receptor tyrosine kinase and STATS signal transduction processes in human breast epithelial MCF-10A cells. p,p'-DDT at physiologically relevant concentrations (i.e. 10 nM) elevated c-erbB2, c-met and STAT1 alpha (p84/91) tyrosine phosphorylation, stimulated Grb2-Sos1 association and elevated MAPK phosphorylation. In contrast, o,p'-DDT under identical conditions failed to stimulate either c-erbB2 or c-met tyrosine phosphorylation, demonstrating a structural specificity for this effect. p,p'-DDT also stimulated breast epithelial cell proliferation, as evidenced by 3H thymidine incorporation and analysis of cell doubling times. These results provide evidence of additional pathways by which environmental chemicals may stimulate cell proliferation and/or tumorigenesis and thereby function as xenomitogens.

Present and future projects of the International Breast Cancer Study Group

The International Breast Cancer Study Group (formerly the Ludwig Group) has conducted nine clinical trials since 1978 (see the Appendix for participants and authors). Biologic hypotheses related to the combined use of chemotherapy and endocrine therapy in women with operable breast cancer were tested. Questions of timing of chemotherapy with respect to tumor surgery and late introduction of chemotherapy were also evaluated. Ongoing and future trials continue in this tradition to investigate combinations of available endocrine therapies and cytotoxic agents.

In vitro sensitivity testing of human breast cancer cells to hormones and chemotherapeutic agents

The sensitivities of human breast cancer cells to hormones and chemotherapeutic agents were measured using a new in vitro assay. Tumor cells from individual patients were cultured on collagen-coated dishes in medium containing the patient's serum. The rationale for use of the patient's serum is that the components of this serum interact with the cells and therapeutic agents in vivo. Cells were incubated for the length of the assay in the presence or absence of estrogen (E2) with or without tamoxifen (TAM) or in the presence or absence of cortisol (F). At 1 day after cell seeding, cells were exposed to a chemotherapeutic agent, Adriamycin, melphalan, or 5-fluorouracil, for 24 h. After a 48-h recovery period, [3H]-thymidine ([3H]-TdR) was added to the cultures for 24 h. Depending on the concentration, E2 generally stimulated or inhibited incorporation of [3H]-TdR into the DNA of cells from estrogen-receptor (ER)-positive tumors. TAM eliminated the effects of E2. F generally stimulated or inhibited incorporation in cells with no correlation to ER status. Stimulation of [3H]-TdR incorporation by hormones increased cell sensitivity to Adriamycin. In contrast, hormone inhibition of [3H]-TdR incorporation decreased cell responsiveness to this drug. This rapid assay, which can measure the sensitivities of breast carcinoma cells to hormones and drugs and identify effective combinations of therapeutic agents, should lead to a rational selection of treatment for the individual patient.