Impact of molecular and histological subtype of breast cancer on ¹⁸FDG-PET/CT imaging: Knowledge gained from recent studies

Over the past few years, several studies have focused attention on the impact of breast cancer (BC) histological subtype or BC phenotype, as defined by hormone receptors (HR) and HER2 status, on the results of FDG-PET/CT at staging, or during neoadjuvant chemotherapy (NAC). At staging, sclerotic bone metastases from invasive lobular carcinoma (ILC) demonstrated low or no FDG uptake in comparison to metastases from invasive ductal carcinoma (IDC). The CT component of PET/CT imaging should be carefully analyzed in the staging of ILC. In patients with triple negative or HER2-positive tumors, the proportion of extraskeletal metastases is high; this must be taken into account in the diagnostic strategy. Staging based on PET/CT findings offers higher prognostic stratification value than that defined by conventional imaging workup. The yield and prognostic information are high in patients with clinical stage IIB or higher. Moreover, the intensity of tumor FDG uptake at baseline may have prognostic value for recurrence, with stronger evidence in HR-positive/HER2-negative phenotype. In the assessment of tumor response to NAC, the metabolic response, generally based on the change in SUV_max (DSUV_max), depends on the BC subtypes. In triple negative BC, a good metabolic response early during NAC has been shown to be predictive of pCR, and the predictive value was reinforced by combining DSUV_max and EGFR status. In 171 patients, no correlation was found between some recently developed PET-derived parameters, i.e. tumor heterogeneity or textural analysis, and BC subtypes. Whether these parameters offer any advantage compared to SUV measurements remains to be demonstrated. (authors)