Multifocal breast cancer and survival: each focus does matter particularly for larger tumours

The objective of this study is to determine whether the aggregate tumour size of every focus in multifocal breast cancer more accurately predicts 10-year survival than current staging systems which use the largest or dominant tumour size.

This study examined the original histological reports of 848 consecutive patients with invasive breast cancer treated in New South Wales (NSW), Australia between 1 April 1995 and 30 September 1995. Multifocal tumours were assessed using two estimates of pathologic tumour size: largest tumour focus diameter and the aggregate diameter of every tumour focus. The 10-year survival of patients with multifocal tumours measured in both ways was compared to that with unifocal tumours.

At a median follow-up of 10.4 years, 27 of 94 patients (28.7%) with multifocal breast cancer have died of breast cancer compared to 141 of 754 (18.7%) with unifocal breast cancer (P=.022). Ten-year survival was not affected by size for tumours measuring 20mm or less, whether or not dominant tumour size (87.9%) or aggregate tumour size (87.0%) was used for multifocal tumours, compared to unifocal tumours (88.1%). For tumours larger than 20mm, 10-year survival was 72.1% for unifocal tumours compared to 54.7% (P=.008) for multifocal tumours using dominant tumour size, but this was 69.5% and not significant when multifocal tumours were classified using aggregate tumour size (P=.49). Multivariate analysis also confirmed the above-mentioned results after adjustment for important prognostic factors.

Aggregate size of every focus should be considered along with other prognostic factors for metastasis when treatment is planned. The current convention of using the largest (dominant) lesion as a measure of stage and associated breast cancer survival needs further validation.