Classification and grading of invasive breast carcinoma.

The main reasons for applying a classification system to invasive breast carcinoma are to obtain a correlation with prognosis and tumour biology. Invasive carcinomas may be sub-divided morphologically according to their degree of differentiation. This is achieved in two ways, by assessing histological type and histological grade. A wide range of histological patterns is recognised in invasive carcinoma of the breast and four broad prognostic groups are recognised: the excellent prognosis group comprises tubular, cribriform, mucinous carcinomas; the good group tubular mixed, mixed ductal NST/special type and classical lobular carcinoma; the average group mixed lobular, medullary and atypical medullary carcinoma and the poor group is composed of ductal NST, mixed ductal and solid lobular carcinoma understanding of the biology of breast cancer. For example, tumours with a medullary phenotype which express basal cytokeratins and are p53 positive and ER and c-erbB-2 negative are strongly predictive of the BRCA-1 gene-mutation carrier state. Histological grading refers to the semi-quantitative evaluation of the morphological structure of breast carcinomas. In the Nottingham method three characteristics of the tumour are evaluated, glandular differentiation, nuclear pleomorphism and mitotic counts. A numerical scoring system on a scale of 1-3 is used to ensure that each factor is assessed individually. Overall grade is assigned as follows: Grade 1: 3-5 points, Grade 2: 6-7 points, Grade 3: 8-9 points. There is a highly significant relationship between histological grade and prognosis; survival worsens with increasing grade. Histological grading has been shown to have good reproducibility and has been adopted for use in Europe, Australasia and the United States. When combined with pathological tumour size and lymph node stage into the Nottingham Prognostic Index there is excellent stratification for patient management.