1. ¹Department of Pathology, Magee-Womens Hospital, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
2. ²Department of Radiation Oncology, Magee-Womens Hospital, University of Pittsburgh Medical Center, Pittsburgh, PA, USA

Correspondence: Dr R Bhargava, MD, Department of Pathology, Magee-Womens Hospital, University of Pittsburgh Medical Center, 300 Halket Street, Pittsburgh, PA 15213, USA. E-mail: rbhargava@mail.magee.edu

^*Current address: Department of Pathology, Regions Hospital, 640 Jackson Street, St Paul, MN 55101, USA.

^†Current address: Department of Pathology and Laboratory Medicine, Chandler Medical Center, University of Kentucky, Lexington, KY 40536, USA.

Received 17 January 2008; Revised 26 March 2008; Accepted 31 March 2008; Published online 9 May 2008.

Abstract

Current literature suggests that strong WT1 expression in a carcinoma of unknown origin virtually excludes a breast primary. Our previous pilot study on WT1 expression in breast carcinomas has shown WT1 expression in approximately 10% of carcinomas that show mixed micropapillary and mucinous morphology (Mod Pathol 2007;20(Suppl 2):38A). To definitively assess as to what subtype of breast carcinoma might express WT1 protein, we examined 153 cases of invasive breast carcinomas. These consisted of 63 consecutive carcinomas (contained 1 mucinous tumor), 20 cases with micropapillary morphology (12 pure and 8 mixed), 6 micropapillary 'mimics' (ductal no special type carcinomas with retraction artifacts), 33 pure mucinous carcinomas and 31 mixed mucinous carcinomas (mucinous mixed with other morphologic types). Overall, WT1 expression was identified in 33 carcinomas, that is, 22 of 34 (65%) pure mucinous carcinomas and in 11 of 33 (33%) mixed mucinous carcinomas. The non-mucinous component in these 11 mixed mucinous carcinomas was either a ductal no special type carcinoma (8 cases) or a micropapillary component (3 cases). WT1 expression level was similar in both the mucinous and the non-mucinous components. The degree of WT1 expression was generally weak to moderate (>90% cases) and rarely strong (<10% cases). None of the breast carcinoma subtype unassociated with mucinous component showed WT1 expression.