Provided herein are methods for determining the presence of cancer (malignant versus benign), monitoring the progression of cancer, monitoring cancer relapse, monitoring the response to cancer therapy, or cancer staging in a subject, by evaluating CD33+/HLA-DRlow, CD14+/HLA-DRlow, CD66b+/HLA-DRlow or, CD11b+/HLA-DRlow MDSC for activation of a transcription factor. Transcription factors include, but are not limited to, STAT3, pSTAT3, HIF1α, or C/EBPβ. The MDSC phenotype can be CD33+HLA-DRlowHIF1α+/STAT3+, CD14+HLA-DRlow HIF1α+/STAT3+/pSTAT3+/C/EBPb+, CD66b+HLA-DRlow HIF1α+/ STAT3+ / pSTAT3+ /C/EBPb+, CD33+HLA-DRlow HIF1α+/ STAT3+ / pSTAT3+ /C/EBPb+, CD11b+HLA-DRlow HIF1α+/ STAT3+ / pSTAT3+ /C/EBPb+, or CD11b+HLA-DRlowC/EBPβ+. Also provided herein are methods for inducing human MDSC from healthy donor peripheral blood mononuclear cells (PBMC) by co-culturing PBMC with human solid tumor cell lines and subsequently measuring their suppressive ability.
