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Ki67 immunohistochemistry, commonly used as a proliferation marker in breast cancer, has limited value for treatment decisions due to questionable analytical validity. The International Ki67 Working Group (IKWG) consensus meeting, held in October 2019, assessed the current evidence for Ki67 immunohistochemistry analytical validity and clinical utility in breast cancer, including the series of scoring studies the IKWG conducted on centrally stained tissues. Consensus observations and recommendations are: 1) as for estrogen receptor and HER2 testing, pre-analytical handling considerations are critical. 2) A standardized visual scoring method has been established and is recommended for adoption. 3) Participation in and evaluation of quality assurance and quality control programs is recommended to maintain analytical validity. 4) The IKWG accepted that Ki67 IHC as a prognostic marker in breast cancer has clinical validity but concluded that clinical utility is evident only for prognosis estimation in anatomically favorable ER-positive and HER2-negative patients, to identify those who do not need adjuvant chemotherapy. In this T1-2, N0-1 patient group, the IKWG consensus is that Ki67 ≤ 5% or ≥ 30% can be used to estimate prognosis. In conclusion, analytical validity of Ki67 IHC can be reached with careful attention to pre-analytical issues and calibrated standardized visual scoring. Currently, clinical utility of Ki67 IHC in breast cancer care remains limited to prognosis assessment in stage I/II breast cancer. Further development of automated scoring might help to overcome some current limitations.

Conjugated linoleic acid (CLA) exhibits multiple biological and molecular activities that have made it the subject of considerable nutrition-related research. Numerous studies support broad acting anti-tumor effects including anti-inflammatory, anti-proliferation, and pro-apoptosis in a variety of model systems. CLA’s ability to influence multiple tumor promoting pathways, without toxicity, may prove valuable in the chemoprevention of breast cancer. The overall objective of this dissertation research was to investigate the potential of CLA in the chemoprevention of breast cancer in a subgroup of women at risk of developing estrogen receptor (ER) negative disease. Overexpression of either the ERBB2 oncogene or the epidermal growth factor receptor (EGFR) is a common event in ER negative breast cancer. To respond to this association, the stated research objective was pursued in relevant model systems. The primary hypothesis was that CLA would downregulate the ERBB2 receptor in vitro and inhibit mammary tumorigenesis in vivo. The t10c12 CLA isomer significantly reduced ERBB2 protein expression in the ERBB2 overexpressing cell line SKBr3. This was accompanied by a decrease in NFκB nuclear localization, cyclooxygenase-2 (COX2)-derived prostaglandin (PG) E2 production, increased apoptosis, and inhibition of proliferation. In contrast to the in vitro data, however 1% dietary CLA had pro-tumor effects in the PyV-mT transgenic mouse model, Mammary gland whole mounts indicated a significant loss of adipose in the CLA-treated group compared to controls that was confirmed by the downregulation of adipocyte-specific genes including PPARγ and adiponectin. CLA’s effect on the adipose was supported by decreases in fatty acid synthase at the protein and mRNA level. cDNA microarray revealed significant downregulation of cytoskeletal and adhesion-related genes in the CLA-treated group. These data suggest CLA’s combined effect on the adipose and epithelial architecture may have promoted