Early metabolic response assessment to neoadjuvant endocrine treatment in ER+, HER2- breast cancer: comparison to the morphological and pathological response.

Objectives To evaluate the value of 18F-FDG PET/CT in the early response assessment of neoadjuvant endocrine treatment for post-menopausal patients (pts) with ER+, HER2- breast cancer. To analyze its prognostic value on overall survival (OS) and distant metastases free survival (DMFS).

Methods This was a prospective and ancillary study of a phase II clinical trial comparing the efficacy of 4 to 6 months anastrozole or fulvestrant in a neoadjuvant setting. PET/CT exams were performed at baseline, after 1 month of treatment (M1: early response) and before surgery (BS: late response) in 11 pts (74.2 years ± 3.6). Pts were classified “metabolic responders” (mR) if SUVmax values decrease was ≥ 40% at M1 or “non-metabolic responders” (mNR) otherwise; late response was also assessed in mR and mNR pts. Early metabolic response was compared to BS morphological response (clinical and MRI), pathological response according to the Sataloff classification, evolution of Ki 67 expression and Allred score during the study and correlated with OS and DMFS.

Results Main results are summarized in Table I. The only patient with a complete metabolic response (BS) had the best pathological response (TB). The Ki 67 value at M1 was lower in mR pts (mR 3.6 %±1.9 vs mNR 8.2%±8; p=0.25). Allred score evolution did not differ between mR and mNR pts. No difference in the early response was observed regarding the histological subtype (ductal or lobular; p>0.05) nor the treatment group (p>0.05). No significant differences were found between mR and mNR pts in OS (p=0.32) and DMFS (p=0.2), but 2 metastatic progressions were observed in mNR pts.

Conclusions These preliminary results show the value of the early metabolic response compared to the morphological response in a neoadjuvant endocrine treatment setting, with a trend to a better prognosis in mR pts.