Uncommon invasive lobular carcinoma with papillary architecture—clinicopathologic and molecular characterization with review of the literature

Breast cancer is the most common malignancy in woman, and its associated mortality is still rising worldwide. Among all the different subtypes of breast cancer, invasive lobular carcinoma (ILC) is the second most frequent. Several histological variants of ILC currently exist such as solid, alveolar, pleomorphic, tubulo-lobular, and mixed types. Recently, a new variant of ILC with a papillary growth pattern has been described. Here, we make a review of the literature and report the sixth case of a woman suffering from this very uncommon variant. Of note, she had a concomitant axillary lymph node metastasis, a manifestation not yet described so far. Molecular analysis showed CDH1 and PIK3CA mutations, along with similar quantitative chromosomal alterations in both primary and metastasis. Because ILC and papillary carcinoma are managed differently, our aim here is to raise awareness among the pathologists to avoid misdiagnosis of this unusual variant and subsequent inappropriate treatment.