Abstract PD16-04: To monitor or not to monitor? MRI monitoring of neoadjuvant chemotherapy effect and its benefit on breast cancer patients’ pathological complete response rate
Authors: Vanovcanova Lucia , Waszulikova Iveta , Krakovska Bibiana Vertakova 
Published: March 2023

Abstract
Introduction: Neoadjuvant chemotherapy (NACT) represents an essential tool for the treatment of selected breast cancer patients aimed to reduce the tumor size for a more conservative resection and to gain early information about the sensitivity to applied treatment. An effective early response assessment helps both to change the therapeutic strategy for patients nonresponding to the treatment used and to avoid the toxicity related to ineffective treatment. We assumed that changing the chemotherapy regimen might avoid the residual cancer burden (RCB) III outcome and lead to the highest possible rate of pathological complete response (pCR) achieved. We examined the benefit of MRI as a preferred method for interim response assessment to NACT with a primary focus on the relation between the pattern of responses to NACT within the MRI- monitored and non-monitored patients and the pattern of final outcomes on the RCB scale. Methods We present a real-life data-based retrospective analysis of 124 female patients with locally advanced breast carcinoma. All patients received NACT (anthracycline-based regimen followed by taxane-based regimen/early switch to taxanes after the 2nd cycle in nonresponders, and antiHER2 therapy if indicated) prior to surgery (mastectomy/breast-conserving surgery, sentinel lymph node biopsy/axillary dissection). Postoperative histopathological analysis of tumor specimens categorised 120 patients according to the RCB scale 0 – III. Four patients had surgery ex muros and were lost to follow-up. Patients were divided into two cohorts. Group A covered monitored patients with pre-treatment MRI and follow-up MRI after the 2nd cycle of NACT. If no response was detected, another follow-up MRI was indicated after the 2nd cycle of a new treatment. Group B comprised patients with no/incomplete MRI monitoring and patients without the change of therapy even though no response was detected by MRI after the 2nd cycle of NACT. Association between categorical variables was tested using chi-square tests. Statistical analysis was performed using StatsDirect® 3.3.5 (StatsDirect Ltd., Cheshire, UK). The data analysis was supported by a grant from the Cultural and Educational Grant Agency of the Ministry of Education, Science, Research, and Sport of the Slovak Republic (KEGA 041UK-4/2020). Results MRI-monitored patients had two times the odds of being RBC 0 (OR = 2.02, P = 0.122) and almost three times the odds of being RCB 0 or RCB I (OR = 2.83, P = 0.0206) than patients with no monitoring. Changing the NACT after the 2nd cycle in the cohort of monitored patients with no response to initial therapy was significantly associated with better outcomes on the RCB scale (P = 0.0042). This result was confirmed by comparing the pattern of results in patients with no response within the group of incompletely monitored patients with known MRI results after the 2nd cycle (P = 0.0257). Changing the ineffective NACT after the 2nd cycle significantly increased the proportion of RCB 0-I by 23.4%, confirming the benefit of response monitoring by MRI. Conclusion Breast cancer constitutes a heterogeneity of tumor subtypes and it is acknowledged that their behaviour during NACT is highly variable and often unpredictable. MRI represents an effective tool for the assessment of tumor response to applied NACT. To achieve the most clinically meaningful impact of the selected treatment it is critical to monitor the tumor response within the first 3 cycles. Our data clearly confirmed that clinical decisions related to the detection of early response or no response (resulting in the change of NACT) lead to better treatment outcomes and less toxicity. The rate of pCR defines the applied treatment efficacy. Every single patient with results different from RCB III has a better prognosis, reduced need for further expensive treatment and also a more favourable quality of life. These key facts need to be carefully considered when discussing the cost and benefits of MRI monitoring.
Citation Format: Lucia Vanovcanova, Iveta Waszulikova, Bibiana Vertakova Krakovska. To monitor or not to monitor? MRI monitoring of neoadjuvant chemotherapy effect and its benefit on breast cancer patients’ pathological complete response rate [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD16-04.