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Background: Metaplastic breast cancer (MBC) is a rare form of breast cancer affecting <1% of breast cancer patients. Previous studies report that the size of MBC is greater than conventional invasive ductal carcinoma at presentation. This may reflect the rapid growth rate of MBC or the difficulty in diagnosis. Imaging characteristics of MBC are not well described but the few published reports suggest that MBC often mimics benign lesions on imaging. The aim of this study therefore is to review the clinical presentation, baseline imaging features, surgical management and final surgical pathology of MBC in a large UK breast cancer unit. Methods: All female patients diagnosed with MBC during the time period Jan 2005-2012 were identified from the pathology database at Leeds University Teaching Hospitals Trust. Pathology reports were reviewed and data on MBC type (following the WHO classification), size, grade, nodal and molecular marker status was extracted. Mammography, Ultrasound (USS), CT and MRI features were recorded. Follow-up was complete until May 2013. Results: 46 patients were identified with a median age of 61yrs and a 5yr survival of 32.6% (median 50 months). Of the 46 cases, 33 presented symptomatically (71.7%), 37 (80.4%) showed a mass on mammography of which 28 (75.7%) was ill defined, 4 (10.8%) well defined and 5 (13.5%) spiculated. All 46 cases had a mass on USS. The imaging score was Bi-rads (Breast Imaging-Reporting and Data System) 5 in 23 cases, Birads 4c in 17 cases and 4a,b in 6 cases. Thirteen patients had MRI. This was performed either to determine disease extent or for neoadjuvant chemotherapy monitoring. All but one of the tumours was seen as a solid mass with some central necrosis the other was seen as an area of nodular enhancement. Nine cases had a staging CT scan for metastatic disease which was negative in all cases.The average size was 28mm (range 11-75mm), 8 (17.3%) were histological grade 3, 5 (10.9%) cases had involved lymph nodes and 28 (60.8%) cases were triple receptor negative. Only 2 cases were HER2 positive. Conclusion: In this series metaplastic cancers were symptomatic in >70%, tended to be large at the time of presentation and only 11% of cases had nodal involvement which is consistent with previous reports. Review of our radiology revealed that all modalities used (mammogram, USS and MRI) reliably showed characteristics suggestive of malignancy. Features suggestive of malignancy include spiculated or irregular ill defined masses on mammography or ultrasound and on MRI large irregular masses with central necrosis and rim enhancement following contrast. These are characteristic or suggestive of malignancy which is contrary to many previous studies of MBC that suggest MBC is difficult to pick up on imaging and commonly exhibits benign features. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-01-08.