Sasada S, et al. - Authors attempted to evaluate the factors causing tumor undetectability on ring-type dedicated breast positron emission tomography (DbPET). For this analysis, an aggregate of two hundred sixty-five patients (288 tumors) underwent DbPET and contrast-enhanced magnetic resonance imaging (MRI) in a prone position. Results revealed that twenty-four tumors (8.3%) were not visualized via DbPET. Outside or at the edge of a field of view (FOV) and insignificant ¹⁸F-fluorodeoxyglucose (FDG) uptake were the two identified factors of undetectable breast cancers on DbPET.