New variant of breast-invasive lobular carcinoma with solid and encapsulated papillary carcinoma growth pattern

Abstract

To date, five cases of invasive lobular carcinoma with solid and encapsulated papillary carcinoma (SPC and EPC) growth pattern were reported. In this article, we describe such a case that might represent a diagnostic pitfall. A 61-year-old woman had a mass on the left breast that was characterized by multiple expansile nodules with a fibrous capsule. Tumor cells were arranged in a solid pattern with inconspicuous delicate fibrovascular cores, some were irregular glandular tubes and papillary, similar to the growth pattern of SPC and EPC. The appearance of the tumor surrounding tissue suggested a special type of lobular carcinoma. The diagnosis of invasive lobular carcinoma was confirmed by immunohistochemistry, which revealed negative E-cadherin, positive cytoplasmic P120, and deleted myoepithelium. Next-generation sequencing revealed CDH1 mutations that further proved the diagnosis of invasive lobular carcinoma. The main differential diagnoses for this tumor are SPC, EPC, neuroendocrine carcinoma, and secretory carcinoma, for which immunohistochemical analysis is an essential diagnostic tool. The growth pattern of invasive lobular carcinoma with EPC and SPC is a variant of the invasive lobular carcinoma newly discovered. The understanding of this variant expands the morphological spectrum of invasive lobular carcinoma and will help prevent misdiagnosis.

Solid papillary carcinoma of the breast

“…22 With regards to breast biomarkers, SPCs show a luminal phenotype (estrogen and progesterone receptor positivity and Her2 negativity) with a relatively simple genome and a few copies of number alterations. 23 Additional genetic features include loss of chromosome 16q and gain of chromosomes 1p and 16p. SPCs are also associated with a higher expression of genes attributing neuroendocrine differentiation, mainly RET, ASCL1 and DOC7.…”

“…SPCs are also associated with a higher expression of genes attributing neuroendocrine differentiation, mainly RET, ASCL1 and DOC7. 23 Table 2 compares the various cases of SPC reported so far in the literature.…”

Diagnostically Challenging Subtypes of Invasive Lobular Carcinomas: How to Avoid Potential Diagnostic Pitfalls

“…In 2016, Rakha et al described three cases of ILC mimicking papillary carcinoma [ 33 ]; this was followed by four more single case reports [ 34 , 35 , 36 , 37 ]. This variant of ILC has been described under different terms such as “ILC mimicking papillary carcinoma” [ 33 ], “lobular breast cancer with solid growth pattern mimicking a solid-papillary carcinoma” [ 34 ], “ILC with papillary features” [ 35 ], “ILC with solid and encapsulated papillary carcinoma growth pattern” [ 36 ], “ILC mimicking encapsulated papillary carcinoma” [ 37 ].…”

“…All patients presented with a palpable lesion. Imaging findings (mammography and ultrasound) showed a well-circumscribed nodular mass in three cases [ 35 , 36 , 37 ] and a hypoechoic, highly vascularized mass in one case [ 34 ]. The tumor size ranged from 1.2 to 5.5 cm (median 2.8).…”

“…In all but one case, a second component with the morphology of a classic variant ILC was found in close relation with the nodular neoplasm. The single case lacking a classic ILC component showed LCIS around the main tumor [ 36 ].…”