ERBB2 and breast cancer: The highest concentration of salivary urea was observed in luminal BC 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.