Relationship between tumor-infiltrating lymphocytes (TIL) and absolute lymphocyte count (ALC) or lymphocyte to neutrophil ratio (LTN) in cholangiocarcinoma (CCA)

343 Background: Tumor microenvironment is potentially a powerful predictive and prognostic marker of immunotherapy. The presence of CD8 TIL has been suggested as a predictive and prognostic marker of PD-1 inhibitor therapy in several malignancies. However, evaluation of TIL is not always feasible especially during or after immunotherapy. Therefore, easily accessible markers are needed for immune monitoring. In CCA, ALC and LTN in peripheral blood have been reported as prognostic factors. We evaluate the relationship between ALC or LTN and CD8 TILs in CCA. Methods: Formalin-fixed paraffin-embedded tumor samples from 41 patients with resected and histologically verified CCA between 1990 and 2015 were identified and immunohistochemically (IHC) stained with anti-CD8. Absolute lymphocyte and neutrophil count of the patients was obtained within 1 week before surgery. The association between ALC, LTN and CD8+ TIL status was investigated using unpaired Student t test and Spearman rank correlation. Results: The median age was 64 (41-85) with 53% male. 22%, 41% and 37% were stage I, II, and III respectively. In CD8 TIL positive, the average ALC was 1764 and in CD8 TIL negative, the average ALC was 2072. There was no significant difference between the two groups (p = 0.38). No difference of LTN was observed between CD8 TIL positive and negative tumors (0.39 vs 0.38, p = 0.69). The correlation between density of CD8 TILs and ALC or LTN was evaluated. No correlation was observed between CD8 TIL density and ALC (R = 0.02, P = 0.3) or LTN (R = 0.02, P = 0.8). Conclusions: ALC or LTN in peripheral blood may not predict CD8 TIL status in patients with CCA.