Myeloid-derived suppressor cells
Myeloid-derived suppressor cells (MDSC) are derived from bone marrow and
can support tumor progression by promoting tumor cell survival,
angiogenesis, invasion of healthy tissue by tumor cells, and
metastases[76]. MDSC consist of two large groups of cells termed
granulocytic or polymorphonuclear (PMN-MDSC), which are phenotypically
and morphologically similar to neutrophils; and monocytic
(M-MDSC)–phenotypically and morphologically similar to
monocytes[77]. It was found that a high percentage of MDSC in EGFR
mutant lung cancer was correlated with poor prognosis and reducing MDSC
can improve the prognosis[78]. In addition, S100A9 positive MDSC
counts in EGFR-TKIs resistant lung cancer was higher than healthy
donors. Further study found that this kind of MDSC could be transformed
into M2 type TAM by activating the RELB gene, thus promoting the
proliferation and metastasis of tumors and resulting in EGFR-TKIs
resistance[65]. At present, there are few studies on the mechanism
of MDSC that participated in EGFR-TKIs resistance. Whether MDSC
inhibition can reverse EGFR-TKIs resistance needs further study.