Cytokeratin 7 negative and cytokeratin 20 positive orbital metastatic breast carcinoma

Abstract Metastatic tumours to the orbit account for only a small proportions of orbital mass lesions and typically come from breast, prostate, lungs or metastatic melanomas. Identifying the source of the primary tumour may represent a challenge, as they are sometimes undiagnosed or the malignancies may sometimes have a different microscopic morphology. In metastatic carcinomas originating from the breast, Cytokeratins and mammary gland specific antibodies are generally informative, showing a classic CK7+, CK20−, Mammaglobin +, GCDFP-15 + profile. Herein, we present a case of breast metastatic tumour to the orbit with an unusual and extremely rare histochemical profile being negative for CK7 and positive for CK20. Our findings highlight the higher sensitivity and specificity of the novel GATA-3 compared with the classic breast immunohistochemical (IHC) markers and advising for careful interpretation of current IHC panels.