Aromatase inhibitors reverse tamoxifen induced endometrial ultrasonographic changes in postmenopausal breast cancer patients

Objective: Aromatase inhibitors may decrease endometrial thickness in breast cancer patients previously having short-term tamoxifen treatment. There is a necessity to find out if aromatase inhibitors can also decrease endometrial thickness in patients previously treated with long-term tamoxifen treatment. Methods: Prospective comparison of the last ultrasonographic endometrial thickness measurement taken before discontinuation of long-term tamoxifen treatment in 36 postmenopausal breast cancer patients, with further measurements, performed following aromatase inhibitors administration. Results: There was a significant decrement of endometrial thickness, following 36.2 ± 16.8 months of tamoxifen treatment, from a mean value of 9.1 ± 5.8 mm, measured at the last ultrasonographic measurement performed before discontinuation of tamoxifen treatment, down to a mean value of 6.0 ± 5.0 mm, measured following 5.8 ± 5.8 months of aromatase inhibitors therapy (P = 0.001). A second ultrasonographic measurement performed in 8 patients following of additional 7.5 ± 4.0 months of aromatase inhibitors treatment revealed further decrement of mean endometrial thickness to 4.8 ± 2.1 mm (P = 0.002 compared to baseline). In 28 patients (77.8%), endometrial thickness was reduced following the administration of aromatase inhibitors, in four patients (11.1%) there was no change in endometrial thickness and four (11.1%) patients demonstrated an increase of endometrial thickness. Conclusions: Aromatase inhibitors may reverse endometrial thickening induced by long-term tamoxifen treatment in postmenopausal breast cancer patients.