Heterogeneity of CD8⁺ tumor-infiltrating lymphocytes in non-small-cell lung cancer: impact on patient prognostic assessments and comparison of quantification by different sampling strategies

Introduction: Infiltration of non-small-cell lung cancer (NSCLC) by CD8⁺ T lymphocytes predicts improved patient survival; however, heterogeneity of intratumoral localization complicates this assessment. Strategies for tumor sampling may not accurately represent the whole tumor. We hypothesized that sampling strategies may alter the identification of tumors with high CD8 density and affect the prognostic significance.

Patients and methods: Twenty-three primary NSCLC tumors were immunohistochemically stained for CD8 and were assessed using automated software with eight different sampling strategies or the whole tumor. Results of all sampling strategies were compared to the whole tumor counts (paired t tests, Pearson's r). Associations between CD8 densities and overall survival were assessed (log-rank test).

Results: Counts from all eight sampling strategies significantly correlated with whole tumor counts (p ≤ 0.001). However, the magnitude of CD8⁺ cell counts and categorization into high vs low infiltrate groups were affected by the sampling strategy. The most concordant values were derived from random sampling of 20 % of the tumor, a simulated core biopsy, or from sampling the tumor center. TIL infiltration was associated with survival when sampling the center (p = 0.038), but not the invasive margin (p > 0.2) or other strategies.

Conclusion: Different tumor sampling strategies may yield discordant TIL density results and different stratification for risk assessment. Small biopsies may be particularly unrepresentative. Random sampling of larger tumor areas is recommended. Enumerating CD8⁺ T cells in the tumor center may have prognostic value.