Background: The quantity, distribution, activation status, cytokine profile, and spatial distribution of tumor-infiltrating immune cells have prognostic value and may be predictive of response to immunotherapies.
Objectives: A survey of relevant immune cell populations including their prognostic significance in the most common types of tumors.
Methods: Nonsystematic assessment and a discussion of studies that were conducted to estimate the prognostic significance of certain immune cell subsets and the methodical approaches used.
Results: For many tumor entities, prognostically favorable and unfavorable immune cell populations can be differentiated. However, nonspecific cell markers that may partly summarize antithetic immune cell subsets can be employed. Differences in sampling procedures and the determination of cut-off levels further limit the comparability of the studies carried out so far.
Conclusion: The phenotypic and functional heterogeneity of tumor-infiltrating immune cells requires the use of cell subset-specific antibodies and antibody combinations. Furthermore, harmonized assessment routines, validation studies, and meta-analyses are important prerequisites for potential diagnostic implementation.
Keywords: Cancer; Immune system; Immunohistochemistry; Leukocytes; Prognostic factors.