Frequency, Clinicopathologic Characteristics, and Follow-up of HER2-Positive Nonpleomorphic Invasive Lobular Carcinoma of the Breast: A Retrospective Analysis of an 11-Year Study in an Academic Institution

Objectives: To investigate human epidermal growth factor receptor 2 (HER2)-positive nonpleomorphic invasive lobular carcinoma (ILC), which has rarely been addressed. Methods: Clinicopathologic characteristics and follow-up of HER2-positive nonpleomorphic ILCs were collected and compared to those of HER2-negative counterparts. Results: Twenty-one cases of HER2-positive nonpleomorphic ILCs were identified, 6.3% of the study population. Compared to HER2-negative nonpleomorphic ILC, patients with HER2positivity were older (P < .05), likely to be hormonal receptor negative (P < .01), and had higher histologic grade and angiolymphatic invasion (P < .01). HER2positivity in nonpleomorphic ILCs was associated with higher recurrence/metastasis with hazard ratio of 2.03 (P < .05). No patient who received neoadjuvant therapy achieved pathologic complete response, and HER2targeted therapy tended to reduce recurrence/metastasis in patients with HER2-positive nonpleomorphic ILC. Conclusions: Our results highlight the existence of HER2 positivity in nonpleomorphic ILCs and reinforce that HER2 is associated with worse prognosis in nonpleomorphic ILC. Key Words: Invasive lobular carcinoma; HER2; Breast