Grading invasive ductal carcinoma of the breast: advantages of using automated proliferation index instead of mitotic count

Breast carcinomas are graded according to the "Nottingham modification of the Bloom-Richardson system" (SBR). The system is hindered, however, by lack of precision in assessing all three parameters including nuclear grade, mitosis, and tubular formation, leading to an element of subjectivity. Our objective was to evaluate a new grading system [the nuclear grade plus proliferation (N+P) system] for subjectivity, ease, and better representation of tumor biology. Its components are nuclear grade and automated proliferation index. Invasive ductal carcinomas, consisting of 137 SBR grade I, 247 grade II, and 266 grade III, were re-evaluated by the N+P system. The two systems were compared with each other and correlated with patients' overall survival, tumor size, angiolymphatic invasion, lymph node status, and biomarker status including estrogen receptor, progesterone receptor, p53, epidermal growth factor receptor, BCL-2, and Her-2. Although there was an agreement between the two systems with histologic and prognostic parameters studied, there was 37% disagreement when grading individual tumors. Fifty-three percent of SBR grade II tumors were "down-graded" to N+P grade I, and 7% were "up-graded" to N+P grade III. Distinction among the different histologic grades for overall survival curves was better indicated by the N+P than the SBR system.