['Calcyclin-binding protein or Siah-1-interacting protein (CacyBP/SIP) is a target protein of the S100A6, which is a member of the S100 family. It has been shown that CacyBP/SIP plays important roles in cell cycle progression, differentiation, and carcinogenesis. The purpose of this study was to explore the correlation of CacyBP/SIP expression and clinical significance in breast cancer.', 'Immunohistochemistry was performed to detect the CacyBP/SIP expression in 79 pairs of breast cancer tissues and adjacent nontumor tissues. Western blot analysis and semiquantitative RT-PCR were used to measure CacyBP/SIP protein and mRNA levels in three pairs of fresh breast cancer tissues and adjacent nontumor tissues. The clinical data were collected by telephone follow-up for 5\xa0years.', 'CacyBP/SIP mRNA and protein levels in breast cancer tissues were significantly higher compared with adjacent nontumor tissues. Poor cellular differentiation, lymph node invasion, and clinicopathological staging in breast cancer were associated with CacyBP/SIP expression. Other factors, such as age, menses, and tumor size, were not related to CacyBP/SIP expression. The up-regulation of CacyBP/SIP expression also was shown to increase recurrence and metastasis of breast cancer and to correlate with short overall survival rate.'] Is cacyBP/SIP expression involved in the clinical progression of breast cancer?