Among them are compounds with anticancer activitydirected at the tyrosine kinase receptor, such as EGFR (erlotinib),20 VEGFR)/EGFR/RET (vandetanib),21 and HER2 (tucatinib),22 as wellas others such as PI3K-δ inhibitor (leniolisib)23 and PI3K-α and PI3K-δ inhibitor (copanlisib).24 Interestingly, in the group of 2-aminoquinazolinederivatives, a chemotype of serotonin receptor ligands for 5-HT5A/5-HT7 can be distinguished (G1A-(S)) (Figure 1).25 Importantly, selective 5-HT5AR antagonists reducethe frequency of tumor sphere-initiating cells in breast cancer celllines.26 Here, EGFR is linked to breast cancer.