Efficacy of Neoadjuvant Chemotherapy in Lobular and Rare Subtypes of Breast Cancer

Objective: To determine the predictive factors for the pathological complete response (pCR) in patients with non-ductal invasive breast cancer (ND-BC) receiving neoadjuvant chemotherapy.Study Design: Observational study.Place and Duration of the Study: Departments of Medical Oncology, Tekirdag Namik Kemal University, Sirnak State Hospital, Aydin Adnan Menderes University, Marmara University, Bakirkoy Sadi Konuk Hospital, Basaksehir Cam and Sakura Hospital, Sakarya University, Balikesir Ataturk Hospital, Turkiye, from April 2016 to December 2022.Methodology: A total of 222 non-metastatic breast cancer patients who received neoadjuvant chemotherapy were included in this retrospective multicentric study. The clinicopathologic data were obtained from the hospitals' electronic-record-system. The logistic regression models were used to identify predictive factors for pCR.Results: One hundred and twenty-six patients (56.8%) had invasive lobular carcinoma and 28 patients (12.6%) had signet ring cell/mucinous carcinoma. A total of 45 patients (20.3%) achieved pCR. The pCR rate was 14.3% for lobular carcinoma and 17.9% for signet ring cell/mucinous carcinoma. The univariate analysis showed that estrogen receptor-negative tumours (p = 0.017), high Ki-67 (p = 0.008), high histologic grade (p<0.001), HER2+ expression (p<0.001), and non-lobular histologic type (p = 0.012) were predictive factors for pCR. The multivariate model revealed that HER2 expression (p<0.001) and Ki-67 (p = 0.005) were independent predictors.Conclusion: Neoadjuvant chemotherapy demonstrated effectiveness in ND-BC patients, leading to favourable pCR rates and enabling breast-conserving surgery. Predictive markers for pCR varied depending on histologic types, with HER2 expression, ER status, Ki-67, and histologic grade showing significance in non-ductal subtypes, while HER2 status alone was predictive in lobular carcinoma.