Abstract P4-02-01: 18F-FDG PET/CT for the assessment of locoregional lymph node involvement and radiotherapy indication in stage II-III breast cancer treated with neoadjuvant chemotherapy

Abstract

Abstract Background: Risk for locoregional recurrence (LRR) in breast cancer depends on tumor size and on number and location of tumor-positive locoregional nodes. Postoperative irradiation of chest wall and/or locoregional nodes is advised in patients at high risk for LRR, but remains controversial in patients at intermediate risk. Because the number of tumor-positive axillary nodes in patients treated with neoadjuvant chemotherapy (NAC) can no longer be determined from the axillary lymph node dissection (ALND) and conventional staging of N3-disease with ultrasound is inaccurate, planning of radiotherapy in these patients is hampered. The aim of the present study was to assess the accuracy of 18F-FDG PET/CT for locoregional staging in stage II-III breast cancer patients scheduled for NAC. Second, we wished to assess the value of pre-chemotherapy PET/CT in estimating the risk for LRR and determining chest wall and/or locoregional radiotherapy indication, based on the detection of ≥4 FDG-avid axillary nodes or occult N3-disease. Methods: 278 patients underwent PET/CT of the thorax in prone position. Presence and number of FDG-avid nodes were evaluated, blinded for other diagnostic procedures. First, PET/CT findings were compared with histopathology before NAC (ultrasound with fine needle aspiration and/or sentinel lymph node biopsy (SLNB)) to determine the diagnostic accuracy for detection of axillary metastases and newly discovered N3-disease. Second, risk estimation and radiotherapy planning were evaluated with and without PET/CT. Conventional locoregional staging consisted of ultrasound with fine needle aspiration before, SLNB before, and ALND after NAC. Patients were classified as low-risk (cT2N0), intermediate-risk (cT0N1, cT1N1, cT2N1, and cT3N0), or high-risk (cT3N1, cT4, cN2-3, and (y)pN2-3) for LRR. Emphasis was on the number of patients upstaged to the high-risk group by PET/CT, requiring postoperative locoregional irradiation. Results: Sensitivity, specificity, positive predictive value, and negative predictive value in the detection of axillary metastases were 80%, 92%, 98%, and 53%, respectively. Occult lymph node metastases in the internal mammary chain and periclavicular area were detected in 17 (6%) and 25 (9%) patients, respectively. PET/CT detected occult N3-disease in 5 (11%) of 47 low-risk patients. In 116 intermediate-risk patients, PET/CT detected ≥4 FDG-avid nodes in 14 (12%) patients and occult N3-disease in 13 (11%) patients, upstaging 25 (22%) of intermediate-risk patients. In total, 30 (18%) of 278 low- and intermediate-risk patients were upstaged to the high-risk group, requiring chest wall and/or locoregional irradiation. Conclusion: In breast cancer patients scheduled for NAC, PET/CT renders pre-chemotherapy SLNB unnecessary in case of an FDG-avid axillary node and detects occult N3-disease in 15% of patients. Pre-chemotherapy PET/CT is a valuable tool for selection of high-risk patients who will benefit from locoregional radiotherapy. In our population, 18% of patients had an indication for locoregional irradiation based on PET/CT information, which was missed by conventional staging. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-02-01.