[Invasive breast lobular carcinoma with extracellular mucin: a clinicopathological analysis]

Objective: To study the clinicopathological features of invasive lobular carcinoma (ILC) of the breast with extracellular mucin and outcomes of patients. Method: Clinicopathological features and clinical follow-up (39-123 months and a median follow-up of 55 months) of seven ILC with extracellular mucin were obtained. Hematoxylin-and-eosin (H&E) and immunohistochemistry (IHC) stained sections were reviewed, and fluorescence in situ hybridization (FISH) assay was performed for tumors with HER2 IHC 2+. Patient prognosis was analyzed and literatures related to ILC with extracellular mucin were reviewed. Results: All seven patients were female, aged from 43 to 73 years (median age, 55 years). The tumors ranged in size from 1 to 5 cm (median size 2 cm). All seven cases were of histological grade 2. Most areas of the tumors presented with the morphology of classic ILC, and variable amount of extracellular mucin were observed focally. In six cases, part of the tumor cells contained intracellular mucin, and the nucleus were pushed to one side of the cells, creating the impression of signet-ring cells. Two patients had lymph node metastases at diagnosis, and developed liver and bone metastases at 38th and 48th month, respectively, after surgery, and died at 48th and 123th month, respectively. While the other five patients, except one lost to follow-up, had been disease-free during the follow-up period. IHC results showed estrogen receptor (ER) and progesterone receptor (PR) positivity in 7/7 and 6/7 cases, respectively. Tumors of six patients were HER2 IHC 0/1+. The remaining one was HER2 IHC 2+, while FISH assay revealed HER2 gene amplification in that tumor. The proportion of cases with HER2-positivity was 1/7. The proliferation index Ki-67 ranged from less than 5% to 30%, and Ki-67 less than or equal to 10% were in 5/7 cases. According to the 2013 St. Gallen International Expert Consensus on breast cancer, all tumors were of luminal types; of those, two were luminal A and five were luminal B. Conclusions: ILC with extracellular mucin tends to occur in women over 50 years old. All tumors in the study are grade 2 classic ILC, with signet-ring cells as a common feature. All seven tumors are classified as luminal types, with luminal B as the main molecular subtype.