Heterogeneity of Invasive Ductal Carcinoma: Proposal for a Hypothetical Classification

To investigate what heterogeneity exists in breast cancer, 228 consecutive patients with operable invasive duetal carcinoma (IDC), not otherwise specified, were categorized on the basis of the horizontal progression model of carcinogenesis. Using the reversed Black's nuclear grade (RBNG) in the IDC component and the association of ductal carcinoma in situ (DCIS), the patients were classified into pure IDC (IDC de novo or ab initio) as Group I, non-high grade (RBNG 1 and 2) IDC with DCIS as Group II, and high grade (RBNG 3) IDC with DCIS as Group III. The Groups classified in the present study appeared as a prognostic factor independent of known prognostic and predictive factors in multivariate test. Group I had the worst prognosis among the three groups and was the most non-responsive to tamoxifen. After performing stratifying analyses by group, it was found that metastasis-free survival was statistically associated with the status of hormone receptors estrogen receptor and progesterone receptor and tamoxifen therapy only in Group II. In addition, the status of c-erbB-2 expression had prognostic significance only within the Group III. Our results may be used to frame an alternative hypothetical model for breast cancer evolution and will lead us to reconsider the tailoring of the comprehensive therapeutic modality used at the present time.