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Breast Tumours Resembling the Tall Cell Variant of Thyroid Papillary Carcinoma: Are They Part of the Papillary Carcinoma Spectrum or a Distinct Entity?

Background: Papillary tumours of the breast are diagnostically challenging lesions and represent a wide spectrum of diseases from papilloma to invasive papillary carcinoma. A rare subtype of breast papillary tumour resembling the tall cell variant of thyroid papillary carcinoma (BTRTPC) has been described. The nomenclature of this entity, its relationship to other papillary tumours, and its nature, whether in situ or invasive, remain unclear. Methods: Seventy-five papillary carcinomas (PCs) of the breast previously diagnosed in routine practice were reviewed and the presence of features (n = 10) characteristic of BTRTPC were assessed to determine whether BTRTPC comprises a distinct entity or is part of the spectrum of the previously defined PC variants. Results: Nuclear overlapping and eosinophilic granular cytoplasm were seen in 81 and 75% of the cases, whereas nuclear grooves, nuclear clearing, and tall cells were noticed in 51, 42, and 38% of the cases, respectively; 27% of the cases showed macro- and micro-follicular architecture filled with colloid-like material. Five cases (7%) lacked oestrogen receptor (ER) expression. Co-existing invasive carcinoma was seen in 25 cases (33%). Two cases displayed several features characteristic of BTRTPC, and both were ER-negative. Conclusion: Features characteristic of BTRTPC overlap with other PCs of the breast. Molecular and immunohistochemical biomarkers are needed to provide objective diagnostic criteria for the characterisation of such lesions in routine practice.