The tumour microenvironment

What is the tumour microenvironment (TME)?

The tumour microenvironment (TME) consists of different cellular, including immune cells, and non-cellular components in and around the tumour. The TME has been recognised to play a significant role in tumour progression.^1,2

Why is the TME important?

The TME shapes tumour evolution (whether the tumour regresses, develops resistance, evades the immune system and/or metastasizes) and consequently impacts patient outcomes.³ An association has been observed between the levels of tumour infiltrating immune cells, key components of the TME, and patient prognosis: a colorectal cancer study showed that higher levels of tumour infiltrating CD3+ immune cells were associated with better disease free survival.⁴

What is the role of PD-L1 in the TME?

Aberrant expression of PD-L1 on tumour cells has been reported to impede anti-tumour immunity, resulting in immune evasion.⁵ Therefore, interruption of the PD-L1/PD-1 pathway represents an attractive strategy to reinvigorate tumour-specific T cell immunity suppressed by the expression of PD-L1 in the TME. This approach has proven effective: PD-L1 expression on immune cells in the TME has been shown to identify urothelial cancer patients who are most likely to benefit from atezolizumab an anti-PD-L1 drug.⁶

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References

NCI Dictionary of Cancer Terms. Tumour microenvironment. http://www.cancer.gov/publications/dictionaries/cancer-terms?cdrid=561725
AACR. The Function of Tumour Microenvironment in Cancer Progression. http://www.aacr.org/Meetings/Pages/MeetingDetail.aspx?EventItemID=73#.V6pCFPkrKaE
Chen F, Zhuang X, Lin L, Yu P, Wang Y, Shi Y, Hu G, Sun Y.BMC Med. New horizons in tumour microenvironment biology: challenges and opportunities. 2015 Mar 5;13:45.doi: 10.1186/s12916-015-0278-7.
Galon J1, Costes A, Sanchez-Cabo F, Kirilovsky A, Mlecnik B, Lagorce-Pagès C, Tosolini M, Camus M, Berger A, Wind P, Zinzindohoué F, Bruneval P, Cugnenc PH, Trajanoski Z, Fridman WH, Pagès F. Type, density, and location of immune cells within human colorectal tumours predict clinical outcome. Science. 2006 Sep 29;313(5795):1960-4.
Blank, C and Mackensen, A, Contribution of the PD-L1/PD-1 pathway to T-cell exhaustion: an update on implications for chronic infections and tumour evasion. Cancer Immunol Immunother, 2007. 56(5): p. 739-745).
Ventana Medical Systems Inc. VENTANA PD-L1 (SP142) Assay. Package Insert. http://www.ventana.com/product/1827?type=2357