The use of human tissue has been approved by the Scientific Ethical Committee of Region Hovedstaden and the Danish Data Protection Agency with reference to H-2-2011-052 and 2011-41-6722, respectively, and patients agreed to donate tissue by written consent. Normal breast tissue was acquired from 29 female donors undergoing reduction mammoplasty for cosmetic purposes. Donors remain anonymous except their ages at the time of surgery. 36 breast carcinoma specimens were donated by women undergoing mastectomy for primary breast cancer. Tissue was cut into pieces for cryo-sectioning or cut finely prior to dissociation using 900 U/ml collagenase solution (Worthington Biochemical) in DMEM/F12 (Gibco) supplemented with 2 mM glutamine and 50 μg/ml gentamycin (Biological Industries) to release epithelial organoids, upon collagenase digestion comprised of epithelium and adjacent stromal cells82 , which were then stored in liquid nitrogen with 90% fetal bovine serum (F7524, Sigma-Aldrich) and 10% dimethyl sulfoxide (D2650, Sigma-Aldrich), which we find, is the optimal condition for freezing, thawing and survival83 (link). Some of the biopsies used in this study have been included in previous studies21 (link),23 (link),28 (link),84 (link).
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