Invasive Lobular Carcinoma Mimicking Papillary Carcinoma: A Report of Three Cases.

UNLABELLED: Encapsulated and solid papillary carcinomas (EPCs and SPCs) are considered historically as a special form of ductal carcinoma in situ. Invasive lobular carcinoma (ILC) is characterised by a discohesive growth pattern. There are several variants of ILC, but, as yet, no papillary subtype has been identified. Here we report 3 cases of ILC presenting as papillary carcinoma (PC) with a typical solid papillary growth pattern. One case was reported on core biopsy as EPC (B5a). The 3 ensuing resection specimens showed features typical of SPC with a circumscribed malignant epithelial proliferation containing fibrovascular cores and surrounded, at least focally, by a thick fibrous capsule. The lobular nature of these tumours was confirmed on the resection specimens by the absence of E-cadherin and ß-catenin membrane expression. The invasive nature was confirmed by the presence of entrapped fat cells, the absence of myoepithelial cells and focal merging of the solid papillary areas with classic ILC at the periphery. Of note, 1 case was a recurrent carcinoma without an in situ component. CONCLUSION: This study provides further evidence that EPC and SPC represent a unique growth pattern of breast carcinomas rather than reflecting the in situ or invasive nature of the tumour, and that ILC can acquire a papillary growth pattern.

Breast Neoplasms with Dermal Analogue Differentiation (Mammary Cylindroma): Report of 3 Cases and a Proposal for a New Terminology.

Salivary gland-like and dermal analogue tumours of the breast are rare lesions that can be diagnostically challenging for pathologists. Data on the clinical behaviour and molecular characterisation of these mammary tumours are limited and their designation is mainly based on similar salivary gland or skin lesions. In this study, we present three cylindromatous breast tumours. These lesions were located within the breast, had ill-defined margins and were composed of nests containing a dual population of cytologically bland cells, surrounded at least partially by basement membrane-like material. The lack of cytological atypia and absence of mitoses led to the diagnosis of benign mammary cylindroma in 1 case. The expression of oestrogen receptor, focal absence of basement membrane material and the focal infiltrative nature together with patchy absence of peripheral basement membrane supported the diagnosis of malignancy in the other 2 cases. We discuss the morphological criteria, immunohistochemical profile and diagnostic pitfalls of these tumours. We also review the literature including previously reported cases of mammary cylindroma and differential diagnoses to be considered before making a diagnosis. We propose the term 'mammary tumours with cylindromatous differentiation', implying their uncertain malignant nature, and propose management strategies.