The effect of tamoxifen and medroxyprogesterone on giant cell formation by monocytes from patients with breast cancer.

Incubation of peripheral blood monocytes from patients with breast cancer under agarose for 6 days at 37 degrees C in a 5% CO2 atmosphere resulted in giant cell formation. This phenomenon appeared to be mediated by retroviruses present in these cells. In this study giant cell formation was investigated in patients with primary stage I and II breast cancer before and 3 months after mastectomy with axillary lymph node clearance. Mastectomy had no significant inhibitory effect on giant cell formation. In vitro incubation of monocytes from patients with breast cancer in the presence of tamoxifen (Nolvadex) resulted in significant inhibition of giant cell formation (P less than 0.000003; paired Student's t-test). In vitro addition of medroxyprogesterone (Farlutal) to monocytes from patients with breast cancer also resulted in significant inhibition of giant cell formation (P less than 0.003: paired Student's t-test). Furthermore, incubation of monocytes from patients treated by mastectomy followed by 3 months treatment with adjuvant tamoxifen, resulted in a significant reduction (P less than 0.00007; paired Student's t-test) in the number of giant cells compared to the same samples tested before the commencement of the treatment. Giant cell formation may be used as a simple test to predicte the response of patients with breast cancer to either tamoxifen or medroxyprogesterone.