Breast cancer is the most common malignancy among women. It remains a major cause of mortality among women, although the five-year survival of breast cancer patients is about 90%. To aid in the clinical treatment decisions, clinical factors and biomarkers are utilized to predict the behaviour and prognosis of breast cancer. Traditionally such prognostic factors have been the size and stage of the tumour, hormone receptor expression, the amplification status of Her2 oncogene and the proliferation activity of the tumour cells.

The purpose of this study is to investigate regulatory proteins of the metaphase-anaphase transition of the cell division and evaluate their potential value in predicting the prognosis of breast carcinoma patients. The study is based on 1135 breast cancer patients with a maximum follow-up time of 22 years. The tissue material was collected into tissue microarrays and the protein expressions were analysed with immunohistochemical and immunofluorescence methods.

Securin, PTTG1IP, separase and SA2 are proteins involved in the regulation of the cell cycle. In this study, the immunohistochemical expression of these proteins in breast cancer tissue was examined. The changes in the expression profile were then used to estimate their prognostic value. Securin overexpression alone predicted a 2.4-fold risk of breast cancer death (p>0.001). Combined with the other studied cell-cycle proteins, this risk was emphasized. A model combining securin, separase and axillary lymph node status increased the risk of breast cancer death 6.2-fold (p 0.0006, CI 3.2-82.6). In addition, cytoplasmic securin expression was associated with triple negative subtype of breast cancer.

Based on this study securin-related cell cycle proteins are promising new candidates as biomarkers for breast cancer prognosis.