Cluster 9 cells are highly similar to cluster 4 in their M2-like macrophage gene expression profile, with the difference being that cluster 9 is highly Gpnmb-expressing, and in tumor-related studies, the tumor-promoting role of myeloid cells is associated with Gpnmb, which can promote cancer cell survival, cancer stem cell expansion and metastatic phenotype acquisition via IL-33(Liguori et al. 2021). The gene discussed is IL33; the disease is cancer.