Feasibility study of FDG PET as an indicator of early response to aromatase inhibitors and trastuzumab in a heterogeneous group of breast cancer patients

Patients with any stage of newly diagnosed or recurrent breast cancer were eligible and enrolled prior to initiation (or resumption) of AI or T therapy. FDG PET and tissue biopsy were planned before and after 2 weeks of AI or T therapy, with pretreatment archival tissue permitted. Cutoffs of ≥20% decline in standardized uptake value (SUV) as FDG PET early response and ≤5% post-treatment expression as Ki-67 early response were defined prior to analysis.Forty-two patients enrolled, and 40 (28 AI, 12 T) completed serial FDG-PET imaging. Twenty-two patients (17 AI, 5 T) had newly diagnosed disease, and 23 (14 AI, 9 T) had metastatic disease (5 newly diagnosed). Post-treatment biopsy was performed in 25 patients (63%) and was either refused or not feasible in 15. Post-treatment biopsy yielded tumor in only 17/25 cases (14 AI, 3 T). Eleven of 14 AI patients with post-therapy tissue showed FDG PET early response, and there was 100% concordance of PET and post-therapy Ki-67 early response. For the T group, 6/12 showed an FDG PET early response, including 2/3 patients with post-therapy biopsy, all with Ki-67 >5%.Substantial changes in FDG PET SUV occurred over 2 weeks of AI therapy and were associated with low post-therapy proliferation. SUV decline was seen in response to T, but few tissue samples were available to test association with Ki-67. Our results support further investigation of FDG PET as a biomarker for early response to AI therapy.Breast cancer is a common, life-threatening malignancy [1]; its biology may be driven by estrogen receptor (ER) expression and/or by overexpression or amplification of the epidermal growth factor family receptor HER2. Endocrine therapies such as aromatase inhibitors (AI) and targeted monoclonal antibodies such as trastuzumab (T; Herceptin？, Genentech, South San Francisco, CA, USA) have dramatically improved breast cancer outcomes for patients with tumors bearing the appropriate marker for response: ER for AIs and HER2 for T. However, n