Multifocal/multicentric breast carcinomas showing intertumoural heterogeneity: a comparison of histological tumour type and Nottingham histological grade of primary tumour and lymph node metastasis.

Our study aimed to compare the histological tumour type and Nottingham histological grade of invasive tumour foci in multifocal/multicentric breast carcinomas with those in corresponding axillary lymph node (LN) metastases. We reassessed slides from consecutive multiple breast carcinomas surgically treated with axillary LN dissection (2007-2012). 155 (19.23%) of 806 cases had multiple breast cancer, of which 115 (74.19%) cases had identical morphology. Of these, 85 (73.91%) cases had axillary LN metastases morphologically identical to the originating breast tumours. 32 of the 40 (80%) cases with different morphology had axillary LN metastases; in most heterogeneous cases with differences in grade (87.5%), the grade of metastases was identical to the grade of the tumour foci with the highest histological grade, and in 33.33% of cases the grade in LN was concordant with the grade of smaller foci. Among the 18 cases heterogeneous in histological type with axillary metastases, 33.33% presented heterogeneous histological types in LN, and 22.22% of them were only concordant with the histological type of the smaller tumour foci. The morphological aspects of axillary LN metastases correspond to the highest histological grade and/or histological tumour type with unfavourable prognosis, which does not necessarily appear in the largest tumour focus.