Response Rates of Invasive Lobular Cancer in Patients Undergoing Neoadjuvant Endocrine or Chemotherapy

Background: A gap remains in the role of neoadjuvant therapy for patients with ILC. Method: Single-institution retrospective review of patients with ILC who received neoadjuvant therapy between 2008 and 2019. Results: 141 patients met inclusion criteria: 71 neoadjuvant chemotherapy (NACT) and 70 neoadjuvant endocrine therapy (NET). 7/71 (9.9%) patients had a pCR following NACT compared to 1/70 (1.4%) with NET (P =.063). pCR was observed in 5/18 (27.8%) patients with Her2Neu-positive disease following NACT, compared to 2/53 (3.8%) with Her2Neu-negative disease (P =.01). For luminal B tumors, median Ki-67 decrease was similar following NACT and NET (18.3 vs 16.3, P =.26). T category decreased in 59 (42.1%) patients following neoadjuvant therapy, increased in 9 (6.4%), and was unchanged in 72 (51.4%). More patients had an increase (28.6%) than decrease (12.1%) in their N category, including 13/60 (21.7%) who were clinically node-negative at diagnosis and identified to have node-positive disease following neoadjuvant therapy, at definitive surgery. Conclusion: In Her2Neu-negative ILC, the potential of a pCR with NACT or NET is low. Most patients’ nodal status and tumor size remain unchanged. There is a potential for pathologic stage to be higher at surgery compared to the clinical stage prior to neoadjuvant therapy.