Purpose  

3′-Deoxy-3′-[¹⁸F]fluorothymidine positron emission tomography ([¹⁸F]FLT-PET) has been developed for imaging cell proliferation and findings correlate strongly with the Ki-67 labelling index in breast cancer. The aims of this pilot study were to define objective criteria for [¹⁸F]FLT response and to examine whether [¹⁸F]FLT-PET can be used to quantify early response of breast cancer to chemotherapy.

Methods  

Seventeen discrete lesions in 13 patients with stage II–IV breast cancer were scanned prior to and at 1 week after treatment with combination 5-fluorouracil, epirubicin and cyclophosphamide (FEC) chemotherapy. The uptake at 90 min (SUV₉₀) and irreversible trapping (K _i) of [¹⁸F]FLT were calculated for each tumour. The reproducibility of [¹⁸F]FLT-PET was determined in nine discrete lesions from eight patients who were scanned twice before chemotherapy. Clinical response was assessed at 60 days after commencing FEC.

Results  

All tumours showed [¹⁸F]FLT uptake and this was reproducible in serial measurements (SD of mean % difference = 10.5% and 15.1%, for SUV₉₀ and K _i, respectively; test–retest correlation coefficient ≥0.97). Six patients had a significant clinical response (complete or partial) at day 60; these patients also had a significant reduction in [¹⁸F]FLT uptake at 1 week. Decreases in K _i and SUV₉₀ at 1 week discriminated between clinical response and stable disease (p = 0.022 for both parameters). In three patients with multiple lesions there was a mixed [¹⁸F]FLT response in primary tumours and metastases. [¹⁸F]FLT response generally preceded tumour size changes.

Conclusion  

[¹⁸F]FLT-PET can detect changes in breast cancer proliferation at 1 week after FEC chemotherapy.