CD14 and lung cancer: A recent study using single-cell RNA-seq in human lung cancer revealed that monocyte/macrophage cells could be divided into four groups (Figure 8) [41]: Group I cells are tissue-resident macrophages that express high levels of cell-cycle-related genes; group III cells are CD14-positive monocytes; group IV cells are CD16-positive monocytes; the remaining cells are broadly classified into group II, which are considered to be derived from circulating monocytes, since these cells express mature macrophage genes and lack transcripts expressed by group I cells.