Tumor progression accompanied by increase in proliferation rate in breast cancer: a preliminary report.

Forty consecutive cases with invasive ductal carcinoma of the breast (samples of both the primary invasive area and the involved node were available for 19 cases, multiple sections of breast tissue including both the primary invasive area and forefront intraductal cancerous area were available for 15 cases; and multiple sections of breast cancerous tissue and the involved node were available for six cases) were examined by immunohistochemical analysis for evaluation of their proliferation rate. In this study, we selected the PCNA index as a marker of the proliferation rate of the tumor cells. We demonstrated that the PCNA index of the primary invasive area was significantly higher than that of the forefront intraductal area (P = 0.0017), and the PCNA index of the involved nodes was significantly higher than that of the primary invasive area (P = 0.0004). These preliminary findings suggest that the progression from the tumor cells of the intraductal cancerous area to the metastatic tumor cells must be accompanied by two phases of increase in the proliferation rate.