Prognostic factors in metaplastic carcinoma of the breast: a multi-institutional study

Abstract

Background: Metaplastic breast carcinoma (MBC) is a rare type of breast cancer that has basal-like characteristics and is perceived to have poorer prognosis when compared with conventional no specific type/ductal carcinomas (ductal/NST). However, current data on MBC are largely derived from small case series or population-based reports. This study aimed to assess the clinicopathological features and outcome of MBC identified through an international multicentre collaboration.

Methods: A large international multicentre series of MBC (no=405) with histological confirmation and follow-up information has been included in this study. The prognostic value of different variables and outcome has been assessed and compared with grade, nodal status and ER/HER2 receptor-matched ductal/NST breast carcinoma.

Results: The outcome of MBC diagnosed in Asian countries was more favourable than those in Western countries. The outcome of MBC is not different from matched ductal/NST carcinoma but the performance of the established prognostic variables in MBC is different. Lymph node stage, lymphovascular invasion and histologic subtype are associated with outcome but tumour size and grade are not. Chemotherapy was associated with longer survival, although this effect was limited to early-stage disease. In this study no association between radiotherapy and outcome was identified. Multivariate analysis of MBC shows that histologic subtype is an independent prognostic feature.

Conclusions: This study suggests that MBC is a heterogeneous disease. Although the outcome of MBC is not different to matched conventional ductal/NST breast carcinoma, its behaviour is dependent on the particular subtype with spindle cell carcinoma in particular has an aggressive biological behaviour. Management of patients with MBC should be based on validated prognostic variables.

Figure 1

Correlation between MBC diagnosed in Western and Asian countries and outcome. (A) Comparison of breast cancer-specific survival (BCSS) of patients with metaplastic breast carcinoma diagnosed Asian countries (upper green curve; 88 patients) and Western countries (lower blue curve; 197 patients) as compared with the control group of conventional ductal carcinoma (middle grey curve; 285 patients) (X²=12.1, DF=2, P=0.002). (B) Comparison of BCSS of same groups after exclusion of locally advanced cases (tumours >stage T2); Asian patients (upper green curve; 63 patients) and Western patients (lower blue curve; 145 patients as compared with the control group of conventional ductal carcinoma (middle grey curve; 285 patients) (X²=2.9, DF=2, P=0.237). A full color version of this figure is available at the British Journal of Cancer journal online.

Figure 2

Association between lymph node stage in MBC and breast cancer-specific survival (node negative (180 patients)=upper blue, node positive 1–3 (46 patients)=middle green and node positive >3 (26 patients)=lower grey) (X²=15.8, DF=2, P<0.0001). The same association was observed in Western and Asian subgroups with or without inclusion of locally advanced cases. A full color version of this figure is available at the British Journal of Cancer journal online.

Figure 3

Association between MBC histologic subtype and outcome. (A) Association between breast cancer-specific survival and MBC histologic subtypes (matrix producing carcinoma (77 cases; upper purple), squamous (74 patients; upper middle green), mixed squamous and spindle (41 patients; lower middle grey) and spindle carcinoma (91 patients; lower blue) (X²=13.9, DF=3, P=0.008). (B) Association between breast cancer-specific survival and MBC histologic subtype analysed as two groups (upper green; matrix producing and squamous combined (151 cases) and lower blue; spindle and mixed spindle and squamous (132 patients); X²=10.8, DF=1, P=0.001). A full color version of this figure is available at the British Journal of Cancer journal online.