Invasive lobular carcinoma with extracellular mucin production—a novel pattern of lobular carcinomas of the breast. Clinico-pathological description of eight cases

Abstract

Invasive lobular carcinoma of the breast is known to produce intracellular mucin and has been recognized in single-case reports to show extracellular mucin production, as well. This latter morphology is not only rare but must also be under- or misdiagnosed. The aim was to better characterize this entity. Cases of lobular cancers demonstrating extracellular mucin formation were identified in a multi-institutional effort and their clinical and morphologic features were assessed. Immunohistochemistry was used to characterize the E-cadherin-membrane complex, neuroendocrine differentiation, and to some extent, mucin formation. All but one of the eight cases occurred in postmenopausal patients. Extracellular mucin production was present in 5 to 50% of the tumour samples and rarely also appeared in nodal and distant metastases. The tumours were completely E-cadherin negative and showed cytoplasmic p120 positivity. The majority (n = 6/8) was also completely negative for β-catenin, but two tumours displayed focal β-catenin positivity in the mucinous area. MUC1 and MUC2 expression was observed in all and 7/8 tumours, respectively; neuroendocrine differentiation was present in only one. Invasive lobular carcinoma with extracellular mucin formation is a rare morphologic variant of lobular carcinoma prone to be misdiagnosed and warranting further studies.

Invasive Lobular Carcinoma of the Breast with Extracellular Mucin: Case Report of a New Variant of Lobular Carcinoma of the Breast

“…We present a case of classic lobular carcinoma but with the rare characteristic of extracellular mucin lakes. This feature is rare but has been documented previously in the literature [ 2 – 7 ].…”

“…The differential diagnoses include pure mucinous carcinoma, mixed mucinous-ductal carcinoma, mucinous carcinoma with neuroendocrine differentiation, mixed lobular and ductal carcinoma, solid papillary carcinoma, and mucocele-like tumor. All these tumors have a ductal phenotype and therefore they express E-cadherin [ 6 , 7 ].…”

“…On the other hand, the aberrant expression of E-cadherin observed in lobular carcinomas is associated with the loss of membranous staining for other molecules of the E-cadherin-membrane complex. Therefore, a study of E-cadherin, β -catenin, and p120-catenin may help in the absence of the characteristic morphological features of ILC [ 7 ].…”

“…We herein report a rare case of ILC with extracellular mucin. To the best of our knowledge, only 13 cases have been reported in the literature [ 2 – 7 ].…”

Synchronous Colonic Adenocarcinoma and Metastatic Lobular Carcinoma in a Colectomy Specimen: A Rare Finding

“…The classical variant displays multifocality, a diffuse architectural, the single-file linear pattern of tumor cells arranged in a concentric or targetoid pattern around normal ducts or structures, and intracellular mucin production either in the form of intracytoplasmic lumina or signet ring cells [ 1 ]. Several variants have been reported in the literature besides the classical ILC, including solid, signet ring cell, tubulolobular, alveolar, trabecular, pleomorphic, and a recently described variant with extracellular mucin production [ 2 ]. The latter variant shows both intra- and extracellular mucin production, a rare feature among breast carcinomas [ 3 ].…”