Response to neoadjuvant chemotherapy as a potential indicator of internal mammary node involvement in early breast cancer.

Abstract

Internal mammary node (IMN) irradiation has the potential to improve the overall survival in nodal positive breast cancer patients. Nevertheless, to achieve these benefits while keeping treatment related morbidity low is technically complex and requires careful patient selection and treatment planning. For this, detection of IMN involvement is of particular importance. This study aims to investigate response of visible IMN to neoadjuvant chemotherapy as potential surrogate for initial IMN involvement. We analyzed 298 non-metastatic breast cancer patients who underwent high-resolution pre-treatment MRI and follow-up MRI after neoadjuvant chemotherapy. If visible IMN were present, diameters were measured in axial and coronal planes on both pre- and post- neoadjuvant chemotherapy (NACT) MRIs. Differences in size were assessed and response systematically classified and correlated with clinical and histopathological response, axillary lymph node metastases (AXN) and tumor characteristics. 175 (58.7%) of 298 breast cancer patients had visible IMN on pretreatment MRI and 158 patients had a histopathological response of the primary tumor. Among these, 62 patients (39.3%) had a response of visible IMN. In patients with AXN the rate of IMN response was particular high with 48.6 %. In patients without AXN 21.8 % of patients with visible IMN showed a response to NACT. Response of visible IMN correlated significantly with medial tumor location and predominant tumor contact with internal mammary perforator vessels (IMPVc). The large majority (76.3 %) of IMN with response to NACT were initially rated as non-suspicious during initial staging and in the interdisciplinary tumor board consensus. Clinical IMN response to NACT may serve as an indicator of previously undetected IMN involvement in a relevant proportion of early breast cancer patients. The observation that approximately 20% of patients without AXN metastases demonstrated a radiologic IMN response warrants further investigation, as this subgroup is not routinely considered for IMN irradiation. These findings highlight the need for prospective validation in larger, well-characterized cohorts using standardized imaging protocols to better define the clinical significance of IMN response to systemic therapy.