ERBB2 and breast cancer: An increase in the concentration of urea in saliva was shown in breast cancer, most pronounced in luminal molecular biological subtypes: luminal A 10.46 [7.69; 12.62] mmol/L (p < 0.0001), luminal B HER2-negative 9.52 [6.72; 12.52] mmol/L (p = 0.0198), and luminal B HER2-positive 8.26 [5.27; 12.07] mmol/L.