Grading breast cancer on microarray samples: comparison with Nottingham grade, and use of boosting classification.

AIMS: Nottingham breast cancer grade (NG) is a subjective morphological assessment based on evaluation of the entire tumour. The value of many novel immunohistochemical and molecular markers is being assessed on tiny microarray samples of tumour and compared with NG. The aim of this study was to investigate whether tumour morphology in microarray samples would correlate with NG. METHODS AND RESULTS: We examined over 40 morphological features in each of 568 breast tumour samples on a microarray obtained from the US National Cancer Institute. Evaluations were subjective, and features were recorded as being present or absent in each tumour. Subsequently, on the basis of binary results, a boosting classification algorithm was implemented to help assign a 'microarray score' and 'microarray grade' to each tumour. Microarray grade was significantly correlated with NG (P < 0.01). High-grade versus low-grade discrepancies were rare (five of 568 samples). CONCLUSIONS: The strong correlation of microarray grade with NG supports pathologist reproducibility in subjective evaluations.