To explore the clinicopathological characteristics of invasive lobular carcinoma (ILC) of the breast with metastases to rare sites.

This study collected clinical data of four patients with rare-site metastatic breast ILC diagnosed in the Department of Pathology, Renmin Hospital of Wuhan University from January 2018 to December 2021. Observations were made on their clinical characteristics, histological morphology, immunohistochemical phenotype and prognosis.

The four cases of rare-site metastatic ILC were diagnosed at the age of 42 to 53 years. The intervals from ILC diagnosis to the first metastasis were 5, 1, 11 and 3 years, respectively. Each case had metastases to different locations (3, 3, 2, 2), including the uterus, adnexa, gastrointestinal tract and peritoneum. Histologically, three cases were classified as classic type and one as pleomorphic type. Based on molecular subtypes, there were three cases of luminal B subtypes and one case of triple negative breast cancer. The clinical treatment strategies involved surgery, chemotherapy and immunotherapy, with endocrine therapy also included for patients with luminal B subtypes.

ILC of the breast has a unique pattern of metastasis. When the metastasis occurs on the organs of the female reproductive system, gastrointestinal tract and peritoneum, there is high risk of misdiagnosis as primary tumors, leading to overtreatment with surgery. The clinicians should pay attention to case history and clinicopathological characteristics in order to make an accurate diagnosis and differential diagnosis.