The aims of this study were to investigate if drug sequence (docetaxel followed by anthracyclines or drugs in reverse order) affects changes in the maximal standard uptake volume (SUVmax) on [18F] flourodeoxyglucose positron emission tomography (FDG-PET) during neoadjuvant chemotherapy in women with locally advanced breast cancer.

Women were randomly assigned to receive either drug sequence and FDG-PET scans were taken at baseline, after four cycles and after eight cycles of chemotherapy. Tumour response to chemotherapy was evaluated based on histology from surgical specimen collected upon completion of chemotherapy.

Sixty women were enrolled into the study. Thirty-one received docetaxel followed by anthracyclines (ARM A) and 29 received drugs in the reverse order (ARM B). Most women (83%) had ductal carcinoma and ten (17%) had lobular or lobular/ductal carcinoma. All but one tumour were downstaged during therapy. Overall, there was no significant difference in response between the two drug regimens. However, women in ARM B who achieved complete pathological response had mean FDG-PET SUVmax reduction of 87.7% after four cycles, in contrast to those who had no or minor pathological response. These women recorded mean SUVmax reductions of only 27% (P<0.01). Women in ARM A showed no significant difference in SUVmax response according to pathological response. Sensitivity, specificity, accuracy and positive and negative predictive values were highest in women in ARM B.

Our results show that SUVmax uptake by breast tumours during chemotherapy can be dependent on the drugs used. Care must be taken when interpreting FDG-PET in settings where patients receive varied drug protocols.

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