Purpose: An increase in the incidence of endometrial cancer and a pote
ntial increase in related mortality has been associated with the admin
istration of 20 mg tamoxifen, the dose adopted in breast cancer chemop
revention trials, thus urging studies on intermediate markers of risk.
Patients and Methods: Thirty-three women who received 20 mg tamoxifen
as adjuvant breast cancer treatment underwent endometrial biopsy. Sam
ples were divided for histologic examination, including a quantitative
analysis of stromal:epithelial ratio, and an assessment of DNA ploidy
and proliferation by flow cytometry, Results were compared with 37 sy
mptomatic subjects. Results: All histograms were DNA diploid, Compared
with controls, a significant increase in the risk of proliferation as
measured by the hyperdiploid fraction was associated with tamoxifen d
uration (less than or equal to 36 months: cumulative odds ratio = 16.5
, 95% confidence interval, 1,85 to 146.5; > 36 months: cumulative odds
ratio = 28.2, 95% confidence interval, 2.56 to 310.6, P for trend < .
05). Tamoxifen-induced risk was significantly reduced by the extent of
menopausal status, No cases of cancer or epithelial hyperplasia were
observed in the tamoxifen group, whereas seven cases of epithelial hyp
erplasia without atypia were observed in the control group. The effect
of tamoxifen on proliferation was associated with an increase in the
stromal component. Conclusion: Tamoxifen at 20 mg/d exerts a time-depe
ndent proliferative effect on the endometrium, particularly in premeno
pausal and early postmenopausal women. This effect appears to be media
ted by the stromal component, which accounts for the discrepancy betwe
en flow cytometry and histology. Our study provides preliminary eviden
ce that the DNA flow cytometric hyperdiploid fraction may be a useful
tool for monitoring endometrial cell proliferation in women exposed to
tamoxifen. (C) 1996 by American Society of Clinical Oncology.