THE PROGNOSTIC EFFECT OF HISTOLOGICAL TUMOR GRADE IN NODE-NEGATIVE BREAST-CANCER PATIENTS

The prognostic effect of histological tumor grade was evaluated in 103 6 patients with early breast cancer (pT1 pN0 M0) entered into a trial comparing mastectomy and breast preserving treatment. All analyses wer e adjusted for the factors treatment, patients' age, and tumor size. T umor grade was defined according to Bloom and Richardson based on the sum of scores assigned to each of three histological features: 1) degr ee of differentiation, 2) pleomorphism, and 3) mitotic index. The rela tive importance of these factors with regard to disease-free survival was evaluated. In univariate as well as in multivariate analyses the p leomorphism was the only factor showing a significant effect (univaria te: p = 0.0024, multivariate: p = 0.015). It was investigated how the factors should be combined to define a histological grading score whic h yields the best possible classification of the patients with respect to prognosis. A new grading system was defined splitting the patients into three groups: 1) pleomorphism 1; 2) pleomorphism 2 or pleomorphi sm 3 and mitotic index 1; 3) pleomorphism 3 and mitotic index 2 or 3. This yields a good classification of the patients with respect to prog nosis (p = 0.0004). The prognostic effect of this score was compared w ith the effects of the grading systems proposed in the literature. Acc ording to Bloom and Richardson and in the modified version by Schauer and Weiss, grading is based on the sum of scores of the various histol ogical factors. Therefore, the strong effect of the pleomorphism was d iluted in these grading definitions (Bloom and Richardson: p = 0.03, S chauer and Weiss: p = 0.028). The grading system proposed by Le Doussa l et al. consists only of the scores of pleomorphism and mitotic index (p = 0.014). In summary, the factor pleomorphism showed a stronger ef fect on disease-free survival by itself than the grading systems propo sed in the literature.