Tumour histological grade may progress between primary and recurrent invasive mammary carcinoma.

AIMS: To assess the constancy of the histological grade of invasive breast carcinomas by comparing primary tumours with their axillary metastases and local or regional recurrences.
METHODS: Eighty four recurrent invasive breast carcinomas with a primary tumour or previous recurrence were available for histological review from the period 1980 to 2000. These and any further recurrences were graded by one observer.
RESULTS: Nine, 24, and 51 tumours with grades 1, 2, and 3, respectively, recurred. Grade 1, 2, and 3 tumours recurred within a median time of 88, 42, and 23 months, respectively. The intraobserver reproducibility of the histological grade was good (kappa = 0.66), and the grades of the primary tumours and their axillary metastases or next recurrence also exhibited good agreement. However, when further (second to sixth) recurrences were included in the analysis, the agreement between the grade of the tumours and their last recurrence was only moderate (kappa = 0.48). Only two of the nine grade 1 and 15 of the 24 grade 2 tumours retained their grade in their last recurrence.
CONCLUSIONS: Low grade carcinomas require a longer follow up. These long term data support the possibility of a transition from low grade invasive breast carcinomas to higher grade tumours. It is suggested that low grade (well differentiated) breast carcinomas are not a single entity: some may progress to high grade tumours, whereas others appear not to progress.