The purpose of this study was to evaluate the effect of the anti-estro
genic tamoxifen (Tx) on the growth of human colorectal cancer cells. M
ethods: Serial concentrations (0.005 mu M, 0.05 mu M, 0.5 mu M, 5 mu M
, and 50 mu M) of the anti-estrogenic tamoxifen (Tx) were added and an
alyzed for their effect on the growth of established human colorectal
cancer cells. HT-29 and SW-620 colon cancer cells and SW-1463 rectal c
ancer cells were rested in both serum-free media and serum-containing
media (10% fetal calf serum). COLO-205 colon cancer and SW-837 rectal
cancer cells were only tested in 10% fetal calf serum-containing media
. Cell growth was measured with the hexosaminidase assay and was compa
red among the different groups. Cells were analyzed for estrogen, rece
ptors using enzyme immunoassay. Results: In serum-free media, Tx inhib
ited the growth of HT-29 (P=.05) and SW-620 (P=.01) colon cancer cells
at all concentrations tested Results: In serum-containing media, Tx i
nhibited (P=.04) the growth of the SW-837 rectal cancer cells at all c
oncentrations and SW-1463 (P=.05) rectal cancer cells at the concentra
tions of 0.05 mu M and 0.5 mu M Tx. The inhibition of cell growth in H
T-29, SW-620 and SW-1463 line was greater (P<.001) under serum-free me
dia conditions Estrogen receptors were not detected in any of the cell
lines tested. Conclusions: Hormonal manipulation with colo-rectal can
cers is possible, but the effect of Tx on the growth of colon cancer c
ells differs from the effect on rectal cancer cells under various cond
itions. The mechanism of inhibition is not clear yet, and further stud
ies are warranted before any clinical implications can be postulated.