Stem cell expansion in ductal carcinoma in situ of breast C. Lopes * , A. Paula, O. Marques, A. Rosa, A. Rema, F. Carvalho * ICBAS, Dept. of Pathology, Porto, Portugal Objective: The aim is to study the ability of a cell marker panel -ALDH1, CD44 and Ki67to identify breast stem cells in no malignant and ductal carcinoma in situ. Method: Double-color triple-immunohistochemistry -to ALDH1, CD44 and Ki 67 -was done in 169 paraffin embedded tissue specimens from 111 patients arrayed in tissue microarray blocks. Statistical was done using Chisquare probability test: differences were considered significant when p<0.05. Results: Significantly higher immunoreactivity was seen in DCIS than in benign lesions of breast (p<0.01) with used markers. In a total of 169 specimens, CD44+/ALDH1+/ Ki67-cells were identied in 110 cases. The distribution was as follows: DCIS (79/57); fibroadenoma (45/29), Atypical hyperplasia (23/13); other benign lesions ( Objective: Data from in vitro and clinical studies suggest that CaSR expression can be associated with the development of bone metastases. Most probably CaSR stimulates production and secretion of PTHRP via EGFR pathway. The aim of our study was to assess expression of CaSR in the primary breast cancer and correlate it with the risk of bone metastases. Method: We have analysed 170 patients with the breast cancer. Bone metastases were diagnosed in 102 cases, 68 patients died without skeletal involvement (control group). CaSR expression was assessed in primary tumors using tissue microarray (TMA) and immunohistochemical technique (polyclonal antibody Pierce Bio. PA1-37213). To evaluate cytoplasmatic CaSR expression we have used 0-1 point scale in which 1 was defined as uniformly strong or medium staining in more than 50 % of tumor cells. Results: Strong or medium staining in more than 50 % was identified in most studied cases, however it was more predominant in patients diagnosed with bone metastases than in the control group (93,14 % vs 83,82 %), p=0,053. Conclusion: Expression of CaSR is common in primary tumors of patients with disseminated breast cancer irrespectively of the metastatic site. However, the patients with bone involvement have higher rate of expression, that is borderline significant statistically. As a result, a group of patients with very high risk of bone dissemination might be separated.