PURPOSE: This study evaluated the ability of 18F-Fluorodeoxyglucose (FDG) and 18F-Fluorothymidine (FLT) imaging with positron emission tomography (PET) to measure early response to endocrine therapy from baseline to just prior to surgical resection in estrogen receptor positive (ER+) breast tumors. METHODS: In two separate studies, women with early stage ER+ breast cancer underwent either paired FDG-PET (n = 22) or FLT-PET (n = 27) scans prior to endocrine therapy and again in the pre-operative setting. Tissue samples for Ki-67 were taken for all patients both prior to treatment and at the time of surgery. RESULTS: FDG maximum standardized uptake value (SUVmax) declined in 19 of 22 lesions (mean 17% (range -45 to 28%)). FLT SUVmax declined in 24 of 27 lesions (mean 26% (range -77 to 7%)). The Ki-67 index declined in both studies, from pre-therapy (mean 23% (range 1 to 73%)) to surgery [mean 8% (range < 1 to 41%)]. Pre- and post-therapy PET measures showed strong rank-order agreement with Ki-67 percentages for both tracers; however, the percent change in FDG or FLT SUVmax did not demonstrate a strong correlation with Ki-67 index change or Ki-67 at time of surgery. CONCLUSIONS: A window-of-opportunity approach using PET imaging to assess early response of breast cancer therapy is feasible. FDG and FLT-PET imaging following a short course of neoadjuvant endocrine therapy demonstrated measurable changes in SUVmax in early stage ER+ positive breast cancers. The percentage change in FDG and FLT-PET uptake did not correlate with changes in Ki-67; post-therapy SUVmax for both tracers was significantly associated with post-therapy Ki-67, an established predictor of endocrine therapy response.

• Keywords
• Aromatase inhibitors, ER+ breast cancer, FDG-PET, FLT-PET, Ki-67,
• MeSH
• Ki-67 Antigen metabolism   MeSH
• Dideoxynucleosides therapeutic use   MeSH
• Adult MeSH
• Fluorodeoxyglucose F18 therapeutic use   MeSH
• Aromatase Inhibitors therapeutic use   MeSH
• Middle Aged MeSH
• Humans MeSH
• Mastectomy MeSH
• Biomarkers, Tumor metabolism   MeSH
• Breast Neoplasms diagnostic imaging   drug therapy   metabolism   surgery   MeSH
• Neoadjuvant Therapy MeSH
• Positron-Emission Tomography MeSH
• Radiopharmaceuticals therapeutic use   MeSH
• Receptors, Estrogen metabolism   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Treatment Outcome MeSH
• Check Tag
• Adult MeSH
• Middle Aged MeSH
• Humans MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• alovudine MeSH Browser
• Ki-67 Antigen MeSH
• Dideoxynucleosides MeSH
• Fluorodeoxyglucose F18 MeSH
• Aromatase Inhibitors MeSH
• Biomarkers, Tumor MeSH
• Radiopharmaceuticals MeSH
• Receptors, Estrogen MeSH