Histology and immunophenotype of invasive lobular breast cancer. daily practice and pitfalls.

Invasive lobular carcinomas (ILC) represent the most common subtype of invasive breast cancer and account for about 5-15% of all breast cancer cases. Invasive lobular carcinoma is often accompanied by in situ lesions, by lobular neoplasia (LN). Invasive lobular carcinomas display diverse histologic patterns varying from classical through solid to pleomorphic subtypes. When analyzing histological subtypes, the classical variant is reported to have a more favorable outcome. The majority of invasive lobular carcinomas are hormone receptor positive, overexpression and/or amplification of the Her2 gene is lower than in carcinomas of invasive ductal type. Loss of heterozygosity of the 16q chromosomal regions and the consequent lack of E-Cadherin expression are common findings in invasive lobular carcinomas. Intra-operative evaluation of resection margins in ILC is often unsatisfactory due to the diffuse nature of the tumor. Size estimation of the invasive component poses a similar challenge in daily practice.