Incidence of brain metastases in lung cancer patients with high PD-L1 expression (>50%) compared to low PD-L1 expression (<1%).

Abstract

e20533 Background: Programmed cell death protein 1 (PD1) is a cell membrane receptor that primarily works to activate T cells and to inhibit the apoptosis process ensuring their longevity. The programmed death-ligand 1 (PDL1) can bind to PD1 and prevent it from carrying out its role, thus disallowing T cells to detect and kill of cancerous cells. It has been widely known that certain types of cancers exploit this mechanism and undergo mutations that overexpress PDL1. A topic of interest for PDL1 is its involvement in brain metastasis. A 2018 study revealed that patients with brain metastasis in non-small cell lung cancer who expressed PDL1 (≥5%) had lower overall survival than patients without PDL1 expression. Another study reported findings highlighting patients with PDL-1 expression displayed higher rates of brain metastasis at the time of diagnosis; however, the data was found to be statistically insignificant. Given the growing interest PDL-1’s role in cancer progression, it is important to assess if expressing PDL1 and to what degree, is related to the progression and development of brain metastasis in lung cancer patients. Methods: In this retrospective study, we inspected data from patients diagnosed with lung cancer (small cell and non-small cell). Multiple data points were collected in a large database. The following data was the focus of our study: progression/development of brain metastasis and PDL1 positivity. Additionally, for patients with PDL1 positivity, we looked at the extent of expression. We explored the association between high (≥50%) vs low (≤1%) PDL1 activity and the progression and development of brain metastasis via a chi-square test. Results: 218 patients were assessed in the database. From these patients, 37 had high (≥50%) PDL1 expression, 25 had moderate expression (1-49%), and 156 had low expression (≤1%). The moderate expression group was not looked at in depth for this study, as the primary interest was largely in the high vs low groups. From the focused data of 193 patients, 5 of the 37 patients (13.5%) of high PDL1 expression group had either progression or development of brain metastasis compared to 35 of the 156 patients (22.4%) in the low expression group. This difference was proven to be statistically insignificant (p=.328). Conclusions: The trend highlights that patients without PDL mutations were more likely to have progression and development of brain metastasis than patients with high PDL1 expression; however, these results were not statistically significant. The findings could be limited by the small number of patients expressing high PDL1 expression. Future directions include identifying whether having any expression of PDL, whether low, moderate, or high confers a significant reduced progression free survival in patients treated with immunotherapy.