Tumour infiltrating lymphocyts (TILs) as an excellent predictive factor for neoadjuvant chemotherapy response on locally advanced rectal cancer patient

Background: In Indonesia, 16,000 new cases of rectal cancer were found in 2020, with a mortality rate up to 50%. Most of the cases were locally advanced rectal cancer which requires neoadjuvant therapy. A predictive marker that can indicate how neoadjuvant therapy is responding is thus required, and TILs is a biomarker that has been extensively studied as a reliable predictive and prognostic marker in colorectal cancer. This study aims to determine if the response to neoadjuvant chemotherapy in locally advanced rectal cancer (LARC) patients correlated with the density of TILs. Methods: This study was a retrospective cohort study with samples taken from rectal cancer patients who visited Dr. Soetomo General Hospital between 2017 and 2021. TILs density measurements were taken from stromal tumors on pre-NAC biopsy examination with H&E staining. Evaluation of chemotherapy response based on abdominal CT scan. The density of TILs using 45% cut-off. Results: A total 38 samples were studied, 21 were male and 17 were female. Twenty-nine samples (86.2%) with weak TILs density showed negative chemotherapy response or progressive tumors. There is a significant correlation between the density of TILs and the chemotherapy response of the sample studied (p=0.002). Conclusion: TILs are an excellent predictive marker for neoadjuvant chemotherapy response in LARC patients and can be examined using H&E staining method which is cheap and fast but still has predictive value.