Objective: The Ki-67 proliferation index has received an important role in treatment tailoring and molecular classification of estrogen receptor-positive breast carcinomas. The aim was to analyze the reproducibility of assessing proliferation on the basis of Ki-67 immunohistochemistry. Methods: Thirty core biopsy samples of breast cancer patients were analyzed after immunostaining with B56, SP6 and MIB-1 monoclonal Ki-67 antibodies. All samples were evaluated twice and independently by 3 pathologists, with each observer performing his daily routine practice. The ratio of Ki-67-positive cells was estimated with 5% accuracy. Correlation was calculated for the results of each investigator for all pairs of antibodies and for the results of each antibody for all pairs of investigators. Ki-67 scores were divided into categories of either 4 quarters or into 3 groups reflecting the St. Gallen consensus recommendations with 15 and 30% as cutoff values. The reproducibility of classifying the tumors into these categories was assessed with ĸ statistics. Results: Altogether, 540 evaluations were made. Good to excellent correlation (Spearman’s and Pearson’s coefficient range 0.74–0.92 and 0.73–0.93, respectively) was noted for the pairwise comparison of antibodies by observer and of observers by antibody. The inter- and intraobserver reproducibility of the Ki-67 score classification into equal quarters (1–25, 26–50, 51–75 and 76–100%) or into 3 categories with cutoffs at 15 and 30% was fair to poor in the middle categories, but moderate to substantial in the low and high ranges. Interobserver differences in practice potentially impacted on less consistent classification. Conclusion: Our results indicate that the three different Ki-67 antibodies tested do not substantially influence the reproducibility of the estimated proliferation rates. Although reproducibility is better in the clinically more relevant distinction of high versus low proliferation, without standardization, the current practice of Ki-67 assessment in many laboratories does not allow proper and consistent therapeutic decision-making.

The lack of oestrogen receptor, progesterone receptor and human epidermal growth factor receptor-2 expression in breast cancer (BC) is the basis for the categorization of the tumour as triple negative breast carcinoma (TNBC). The majority of TNBCs are aggressive tumours with common metastases and decreased expression of markers that could help in identifying the metastatic lesion as of mammary origin. Breast markers, such as gross cystic disease fluid protein-15 (GCDPF-15), GATA binding protein 3 (GATA3), mammaglobin (MGB) and SOX10, are not uniquely specific to BC. Our aim was to evaluate trichorhinophalangeal syndrome type 1 (TRPS1) protein as a breast marker in a series of cytokeratin-5-expressing TNBC, mostly corresponding to basal-like TNBCs, previously characterized for the expression of other breast markers. One hundred seventeen TNBCs in tissue microarrays were immunostained for TRPS1. The cut-off for positivity was ≥ 10%. The reproducibility of this classification was also assessed. TRPS1 positivity was detected in 92/117 (79%) cases, and this exceeded the expression of previously tested markers like SOX10 82 (70%), GATA3 11 (9%), MGB 10 (9%) and GCDFP-15 7 (6%). Of the 25 TRPS1-negative cases, 11 were positive with SOX10, whereas 5 to 6 dual negatives displayed positivity for the other makers. The evaluation showed substantial agreement. Of the five markers compared, TRPS1 seems the most sensitive marker for the mammary origin of CK5-expressing TNBCs. Cases that are negative are most often labelled with SOX10, and the remainder may still demonstrate positivity for any of the 3 other markers. TRPS1 has a place in breast marker panels.

In previous studies we found that uveal melanoma cells grown in extracellular matrix (ECM)-containing three-dimensional (3D) cultures have increased resistance against herpes simplex virus type 1 (HSV-1)-mediated destruction relative to cells cultured without ECM. Using additional tumor cell types including MB-231 human breast cancer cells, PC-3 human prostate cancer cells, and P19 mouse embryonal carcinoma cells, we show here that tumor cell lines other than melanoma are also more resistant to HSV-1-mediated destruction in 3D cultures than cells grown in 2D. We also demonstrate here that one mechanism responsible for the increased resistance of tumor cells to HSV-1 infection in 3D cultures is an ECM-mediated inhibition of virus replication following virus entry into cells. These findings confirm and extend previous observations related to the role of the ECM in tumor resistance against HSV-1 and may lead to improved strategies of oncolytic virotherapy.

Classic diffusely infiltrating lobular carcinoma has imaging features divergent from the breast cancers originating from the terminal ductal lobular units and from the major lactiferous ducts. Although the term “invasive lobular carcinoma” implies a site of origin within the breast lobular epithelium, we were unable to find evidence supporting this assumption. Exceptional excess of fibrous connective tissue and the unique cell architecture combined with the aberrant features at breast imaging suggest that this breast malignancy has not originated from cells lining the breast ducts and lobules. The only remaining relevant component of the fibroglandular tissue is the mesenchyme. The cells freshly isolated and cultured from diffusely infiltrating lobular carcinoma cases contained epithelial–mesenchymal hybrid cells with both epithelial and mesenchymal properties. The radiologic and histopathologic features of the tumours and expression of the mesenchymal stem cell positive markers CD73, CD90, and CD105 all suggest development in the direction of mesenchymal transition. These hybrid cells have tumour-initiating potential and have been shown to have poor prognosis and resistance to therapy targeted for malignancies of breast epithelial origin. Our work emphasizes the need for new approaches to the diagnosis and therapy of this highly fatal breast cancer subtype.