Pre-chemotherapy 18F-FDG PET/CT upstages nodal stage in stage II-III breast cancer patients treated with neoadjuvant chemotherapy.

In breast cancer patients treated with neoadjuvant chemotherapy (NAC) the number of tumor-positive nodes can no longer reliably be determined. Furthermore, ultrasound (US) seems suboptimal for the detection of N3-disease. Therefore we assessed the proportion of breast cancer patients treated with NAC in which pre-chemotherapy 18F-FDG PET/CT detected ≥4 axillary nodes or occult N3-disease, upstaging nodal status and changing risk estimation for locoregional recurrence (LRR). Conventional regional staging consisted of US with fine needle aspiration and/or sentinel lymph node biopsy. Patients were classified as low-risk (cT2N0), intermediate-risk (cT0N1, cT1N1, cT2N1, cT3N0), or high-risk (cT3N1, cT4, cN2-3) for LRR. The presence and number of FDG-avid nodes were evaluated and the proportion of patients that would be upstaged by PET/CT, based on detection of ≥4 FDG-avid axillary nodes defined as cN2(4+) or occult N3-disease, was calculated. In total, 87 of 278 patients were considered high-risk based on conventional staging. PET/CT detected occult N3-disease in 5 (11 %) of 47 low-risk patients. In 144 intermediate-risk patients, PET/CT detected ≥4 FDG-avid nodes in 24 (17 %) patients and occult N3-disease in 22 (15 %) patients, thereby finally upstaging 38 (26 %) of intermediate-risk patients. Of 43 (23 %) upstaged patients, 18 were ypN0, 12 were ypN1, and 13 were ypN2-3. Pre-chemotherapy PET/CT is valuable for selection of breast cancer patients at high risk for LRR. In our population, 23 % of patients treated with NAC were upstaged to the high-risk group based on PET/CT information, potentially benefiting from regional radiotherapy.