Predictive and prognostic value of FDG-PET/CT imaging and different response evaluation criteria after primary systemic therapy of breast cancer

Objectives: (1) To predict pathological complete remission (pCR) and survival after primary systemic therapy (PST) in patients diagnosed with breast cancer by using two different PET/CT based scores: a simplified PERCIST-based PET/CT score (Method 1) and a combined PET/CT score supplemented with the morphological results of the RECIST system (Method 2) and (2) to assess the effect of different breast carcinoma subtypes on tumor response and its evaluation.

Methods: Eighty-eight patients were enrolled in the study who underwent PET/CT imaging before and after PST. PET/CTs were evaluated by changes in maximum Standardized Uptake Value (SUVmax) and tumor size. Method 1 and 2 were applied to predict pathological complete remission (pCR). Kaplan-Meier analyses for survival were performed. Classification into biological subtypes was performed based on the pre-therapeutic tumor characteristics.

Results: A total of 30/88 patients showed pCR (34.1 %). Comparing pCR/non-pCR patient groups, significant differences were detected by changes in SUVmax (p < 0.001) and tumor size (p < 0.001) regarding the primary breast lesions. To predict pCR, Method 2 had higher sensitivity (72.4 % vs. 44.8 %) and negative predictive value (57.9 % vs. 45.8 %) with lower false negativity rate (16 vs. 32) than Method 1. pCR rate was higher in Her2-positive and triple negative tumors. Despite the significant differences detected between the biological subtypes regarding changes in primary tumor SUVmax (p = 0.007) and size (p = 0.015), the subtypes only had significant impact on response evaluation with Method 2 and not with Method 1. In our study, neither clinical nor pathological CR were predictors of longer progression-free survival.

Conclusions: Our results suggest that combined PET/CT criteria are more predictive of pCR. The effect of biological subtypes is significant on pCR rate as well as on the changes in FDG-uptake and morphological tumor response. Response evaluation with combined criteria was also able to reflect the differences between the biological behavior of breast tumor subtypes.