By Nicole Zhao ’20

Numerous cancer research projects are dedicated to investigating the primary tumor and its microenvironment. Though this is undoubtedly important, the role of immune cells during cancer dispersion in the blood cells is largely uncharacterized. Circulating tumor cells (CTCs) lead to metastasis of several types of cancers and its levels are often a predictor of survival rate. These cells are often found associating with non-malignant white blood cells. The identity, relationship, and function of white blood cells often found with circulating tumor cells is largely unknown.

In a recent study, white blood cells that were associated with circulating breast cancer cells were isolated from capillary blood samples from both patients and mouse models. Both the cancer cells from the primary tumor and the CTCs were characterized via cell-surface markers. It was found that 85.5 – 91.7% of the white blood cells that were associated with CTCs were found to be neutrophils. Furthermore, single-cell RNA sequencing identified several active genes in neutrophil-associated CTCs that contributed to more efficient metastasis than CTCs not associated with neutrophils. The study also found that clusters of neutrophils associated with CTCs were most efficient with metastasis and are associated with poor prognosis.

These novel characterizations provide insight into the interactions between CTCs and immune cells, which present vulnerabilities of the metastatic process. Since neutrophils directly aide CTCs in cell cycle progression and increase their metastatic potential, CTC-neutrophil clusters could be a target rationale for future cancer therapies that prevent or delay metastasis in breast cancer and other pathologies.
References

1. B. Szczerba, et. al., Neutrophils escort circulating tumour cells to enable cell cycle progression. Nature, (2019). doi: 10.1038/s41586-019-0915-y.  
2. Image retrieved from: https://www.flickr.com/photos/nihgov/40379829875