Abstract P5-02-01: Discrepancy between CT and FDG-PET/CT in the staging of patients with inflammatory breast cancer: Implications for radiation therapy treatment planning

Background: To compare suspected areas of cancer involvement based on the findings of CT and FDG-PET/CT in patients with inflammatory breast cancer (IBC) and to determine if discrepancies would modify radiation therapy treatment fields. Methods: This is a retrospective study of 29 consecutive female patients with IBC (median age 49 years, range 28–78) who had both CT and PET/CT scans prior to the initiation of systemic therapy. CT and PET/CT scans were obtained within a median of 3 days (range 0–64). CT and PET/CT scans were independently reviewed by a board-certified radiologist (PD) and a board-certified nuclear medicine physician (HJ), respectively. Findings were recorded by anatomic site and graded as negative, equivocal or positive for malignancy. Radiation fields were then determined by a breast radiation oncologist (JB) after separately reviewing the CT and PET/CT images. Discrepancies between the two modalities were recorded. The study was approved by the hospital institutional review board. Results: Seven of 29 patients (24%) had discrepant findings that likely would have resulted in a modification of radiation treatment fields and/or radiation dose. In four patients, internal mammary nodal involvement was suspected on PET/CT but not on CT. In two of these four patients, PET/CT also detected additional disease (supraclavicular in one patient and chest wall in the other) that likely would have required a change in radiation field and/or dose. Another patient had subpectoral adenopathy on PET/CT that was not considered abnormal on CT. One patient had equivocal findings in the infraclavicular region on CT which was negative on PET/CT. In one patient, body habitus limited the CT evaluation; more extensive infiltrative soft tissue and nodal disease was seen on PET/CT. In four patients, there were discrepant findings for distant disease that likely would have resulted in a change in management or additional imaging studies. In two of these cases, PET/CT showed a clearly positive finding that was negative or equivocal on CT. In an additional two cases, equivocal PET/CT findings would have resulted in additional testing that would not have been recommended by CT alone. In another 4 cases, metastatic disease was suspected based on CT, but additional sites (all in bone and not seen on CT) were suspected on PET/CT. Conclusions: Inflammatory breast cancer patients have a high probability of presenting with extensive local/regional disease and distant metastases. In our IBC population, PET/CT imaging would have likely resulted in a change of radiation field or dose in 7 of 29 (24%) patients. Additionally, in four instances PET/CT suspected additional metastatic disease (14%). These discrepancies most commonly involved inclusion of an internal mammary nodal radiation field and identification of distant metastases. Pathologic verification of abnormal findings is necessary to verify these results. PET/CT imaging should be considered a standard component of radiographic staging for patients with IBC. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-02-01.