Comparison of first-course PET scan against fourth-course MRI for early detection of poor responders to neoadjuvant chemotherapy (NAC) for breast cancer (BC).

564 Background: Pathologic CR or near CR after NAC is associated with excellent clinical outcome. However, some patients fail to respond, thus receiving unnecessary NAC that could lead to progression prior to surgery. Early identification of drug resistance can prompt discontinuation or early modification of ineffective NAC. We compared predictive value of an early 18FDG-PET/CT scan after first NAC course and MRI after 4 courses of NAC. We then evaluated their correlation with pathologic response. Methods: Pts with localized invasive BC ≥2 cm were eligible. MRI and 18FDG-PET/CT scan were performed at baseline. PET was repeated two weeks after course 1 of anthracycline-based NAC. SUVmax were compared with baseline. We measured the % drop in SUVmax after course #1 NAC and % reduction in size of largest diameter by MRI after course #4. We used the M. D. Anderson Residual Cancer Burden (RCB) tool (JCO 25:4414, 2007), which calculates the degree of pathologic response using a formula to measure the amount of r...