Diagnostic difficulty arising from displaced epithelium after core biopsy in intracystic papillary lesions of the breast.

This study reports two cases of intracystic papillary carcinoma of the breast, which had been biopsied preoperatively using a 14 gauge (14G) core biopsy needle. In each case, a needle tract containing groups of epithelial cells within granulation tissue could be identified on histology of the excised specimen. Both cases showed extracapsular tumour, which was interpreted as displacement of epithelium related to preoperative core biopsy. Subsequent axillary lymph node sampling showed no evidence of metastasis. In one case, extracapsular tumour appeared to be in blood vessels, but flattened cells lining the spaces containing tumour failed to react with factor 8 related antigen or CD34 on immunohistochemistry. It is likely that intracystic papillary carcinomas are particularly prone to this artefact because friable tumour fragments escape, accompanied by cyst fluid, when the capsule is punctured by a 14G core biopsy needle.