Descriptive clinicopathologic study of 17 patients with endometrial cancer during or after adjuvant tamoxifen in early breast cancer.

BACKGROUND

Studies have shown that patients with early-stage endometrial cancer who have previously used endogenous estrogen (oral contraceptives or estrogen replacement therapy) have a favorable prognosis. This has not yet been demonstrated for patients with early-stage endometrial cancer who have received tamoxifen. In addition, studies have raised the question of whether women receiving tamoxifen are at increased risk of endometrial cancer.

PURPOSE

Our aim was to determine whether the prognosis is favorable for patients with diagnosis of endometrial cancer after adjuvant treatment with tamoxifen for breast cancer.

METHODS

We matched 931 patients from the Stockholm Adjuvant Tamoxifen Trial in early breast cancer against the Swedish Cancer Registry and identified 17 who subsequently had endometrial cancer. These patients had been randomly assigned to receive 40 mg/d tamoxifen orally for 2 years beginning 4 weeks after surgery for breast cancer. Histologic specimens, patient records, and death certificates were reviewed to verify treatment and causes of death.

RESULTS

Thirteen of the 17 patients diagnosed with endometrial cancer were alive; for three of the four who had died, the cause of death was endometrial cancer. All 16 evaluable tumors except one were World Health Organization (WHO) histologic grades I-II. Only one patient had advanced disease (stage IV); the remaining tumor was a mixed mesodermal malignant tumor that could not be classified under the WHO grading system. Median time for adjuvant tamoxifen use was 24 months (range, 6-60 months) with a median cumulative tamoxifen dose of 29 g (range, 7-72 g). Median time from initiation of adjuvant tamoxifen to diagnosis of endometrial cancer was 32 months (range, 6-130 months). Ten-year actuarial survival after diagnosis of endometrial cancer for the 17 patients treated with tamoxifen was 73%.

CONCLUSION

Because of the small number of patients, our results do not rule out the possibility of a favorable prognosis for patients with a diagnosis of endometrial cancer following tamoxifen treatment.

IMPLICATIONS

The incidence of secondary endometrial cancer reported in this study following treatment of breast cancer patients with tamoxifen at doses of 40 mg/d in a large clinical trial is higher than that reported for previous large trials of tamoxifen at doses of 20 mg/d. Thus, tamoxifen dosage may be a critical factor in the subsequent occurrence of endometrial cancer. Our results also suggest two important considerations for improved follow-up in long-term tamoxifen trials: careful registration of second cancers and routine gynecologic examinations to ensure early detection of endometrial cancer.