Abstract PO4-07-12: Concordance of Breast ultrasound (US) and breast Magnetic resonance imaging (MRI) for local (tumor size and node involvement) staging in patients with breast cancer before neoadjuvant chemotherapy treatment (NACT)

Abstract Introduction Breast cancer is the main cause of cancer-related deaths in Colombia, with many patients diagnosed with locally advanced (LABC) or metastatic disease. In the locally advanced setting, the use of NACT offers the opportunity of downstage BC and allows to adjust therapy based on the response, but, considering emerging therapies available in LACB as immunotherapy in triple negative BC (TNBC), dual HER2 blockade in HER2 positive BC or adjuvant iCDK 4/6 in luminal BC the importance of accurate pre NACT staging has become critical, we aim to explore the concordance of US and MRI as a method of BC staging in the NACT setting. Methods: EVA (Evidence – Verification – Analysis) is a prospective institutional multi-tumor registry that aims to gather demographic, clinical, and genomic variables from patients treated at Fundación CTIC, in Bogota Colombia, based on this registry, we recover the data from the patients that were treated with NACT and were staged with a US and an MRI before the initiation of treatment, dis concordance between the two methods was establish if a different Tumor size (change from T2 to T3 for example), a different node stage (chance from N2 to N2) or the discordant detection of multifocal disease, a descriptive analysis were performed. Results: 30 Patients were included in the analysis, The mean age was 51,7 years (28 – 79), 15/30 patients were ER of PgR positive BC, 11/30 HER2 positive BC (7/11 HER2 positive and 4/11 Luminal B HER2 positive) and 4/30 were TBNC. 28/30 patients were ductal carcinoma, with 1/30 lobular carcinoma and 1/30 medullary carcinoma. Mean ADC in luminal A-like BC was 0,9, 0,66 (0,4 – 0,9) in luminal-B HER2 negative BC, 0,77 (0,4 – 0,9) in HER2 positive BC, and 0,83 (0,7 – 0,9) in TNBC Concordance between US and MRI was only seen in 14/30 patients. The causes of discordance were Tumor size on 9/16 (change from T2 to T3 or evidence of pectoral muscle involvement), node staging on 11/16 (8/11 patients were node down staged based on MRI image), and evidence of multifocal disease not seen in the US on 2/16. Conclusion: Considering the high discordance rate between US and MRI, and the implications of accurate staging before NACT, we think that MRI should be considered as a routine evaluation before NACT. This is a small sample so a larger cohort would be needed for confirmation of this observation, based on the design of EVA, we expect to further evaluate the significance and uses in the NACT setting. Citation Format: Aura Pareja, Sergio Cervera, Maria Bravo, Sandra Franco, Jose Caicedo, William Mantilla. Concordance of Breast ultrasound (US) and breast Magnetic resonance imaging (MRI) for local (tumor size and node involvement) staging in patients with breast cancer before neoadjuvant chemotherapy treatment (NACT) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-07-12.