Reply to: Oestrogene receptor expression level may affect mammographic density changes following discontinuation of tamoxifen in premenopausal women with oestrogen receptor-positive breast cancer
by Won Hwa Kim, Nariya Cho (river7774@gmail.com)
Kim, W.H., Cho, N., Kim, YS. et al. Eur Radiol (2018). https://doi.org/10.1007/s00330-017-5293-yReply to Letter to the Editor: Oestrogene receptor expression level may affect mammographic density changes following discontinuation of tamoxifen in premenopausal women with oestrogen receptor-positive breast cancer
Dear Editor,
We thank the authors for their interest in our cited article “Mammographic density changes following discontinuation of tamoxifen in premenopausal women with estrogen receptor-positive breast cancer [1]”.
We agree with the author’s comment that the level of estrogen receptor (ER) expression of breast cancer could affect sensitivity of tamoxifen treatment to breast cancer. In addition to the study by Prabhu JS et al. [2], Kim et al. has demonstrated that low-level expression of estrogen receptor (ESR1) mRNA expression is a determinant of tamoxifen resistance in ER-positive tumors [3]. However, we did not analyze the association between the level of ER expression of breast cancer and the density changes after tamoxifen treatment or discontinuation. In addition, we believe that the level of ER in normal breast tissue rather than that of breast tumor might affect breast density change after tamoxifen treatment or discontinuation, because breast density change is usually measured based on contralateral (unaffected, normal) breast tissue. Previous studies have reported that the actual percentage of positive cells that stain for ER ranges from < 5% among premenopausal women to 26% positive cells among postmenopausal women [4-6]. This variation of the level of ER in normal breast tissue might affect the breast density changes following tamoxifen treatment or discontinuation. Future studies to investigate the association between the level of ER in normal tissue or breast tumor and density changes following tamoxifen discontinuation would be interesting.