Invasive Lobular Carcinoma Mimicking Encapsulated Papillary Carcinoma with a Literature Review: A Rare Variant Detected Serendipitously.

Invasive lobular carcinoma with papillary features is a newly proposed variant which presents as a relatively well-circumscribed mass lesion with at least partial peripheral thickened fibrous capsule and central delicate fibrovascular cores, morphologically mimicking encapsulated papillary carcinoma or solid papillary carcinoma. There are only 5 cases described in literature. We here report an interesting example of invasive lobular carcinoma with papillary growth pattern surrounded by a thick fibrous capsule, mimicking encapsulated papillary carcinoma (EPC). The lobular nature of the tumor was confirmed by the absence of membranous expression of E-cadherin and p120 catenin. The lobular cytological features are subtle in this variant and may be overlooked. Differentiation of this variant from papillary carcinomas is crucial for correct tumor categorization, staging and most importantly, proper treatment.