The prognostic significance of inflammation and medullary histological type in invasive carcinoma of the breast

Abstract

The new gene expression molecular taxonomy of breast cancer places medullary carcinoma in the basal group. The basal group is considered to have a poor prognosis, but medullary carcinoma is considered to have a better prognosis than other grade 3 carcinomas. The prognostic significance of tumour associated inflammation, an important feature of medullary carcinomas, remains controversial. The aim of this study was to assess the prognostic importance of medullary histological type and inflammation in breast cancer. One thousand five hundred and ninety-seven patients who received no systemic adjuvant treatment and who had a median follow up of 9.5 years were studied.

Results: Prominent inflammation was associated with high histological grade and with better survival [relative risk (RR) 0.57, 95% confidence intervals (CI) 0.44-0.74] on multivariate analysis. Typical and atypical medullary carcinomas (n=132) did not have significantly different survival and were grouped together. Medullary carcinoma did not have significantly different prognosis than grade 3 ductal carcinoma with prominent inflammation, but both had a better prognosis than grade 3 ductal carcinoma without prominent inflammation (P<0.0001 and P=0.03). These differences were independent of other prognostic factors. These results question the current separation of typical and atypical medullary carcinoma. Prominent inflammation is associated with a better prognosis, and may explain the better prognosis in medullary carcinoma compared with grade 3 ductal carcinoma without prominent inflammation. The good prognosis of medullary carcinoma emphasises the heterogeneity of basal-like breast carcinomas. Further studies are needed to investigate the difference in survival between medullary carcinoma and other forms of basal carcinomas and the role of inflammation in any such differences in behaviour.