Introduction: The expression status of immune markers are of current research interest due to their potential roles as predictive biomarkers for immunotherapy in cancers. Currently there is little information on how the microenvironment of tumors and/or therapy-inducible histological transformation may affect the expression of these immune markers. Methods: A 76-year-old never-smoking female with epidermal growth factor receptor (EGFR) mutated lung adenocarcinoma (AC) acquired resistance to gefitinib. After her death, autopsy revealed small-cell lung cancer (SCLC) transformation and EGFR T790M secondary mutation as mutually exclusive resistance mechanisms. Two liver metastases (SCLC vs. AC with T790M) and two lymph node metastases (SCLC vs. AC with T790M) were analyzed to compare the expression status of immune markers by immunohistochemistry (IHC) and an immune-oncology gene expression panel (HTG EdgeSeq Immuno-Oncology Assay). Results: IHC analysis revealed that PD-L1 was expressed in 5% of tumor cells with AC histology (T790M) but not in tumor cells with SCLC transformation (Table 1). The liver metastasis with SCLC transformation showed negative stromal PD-L1 expression and scant tumor infiltrating lymphocytes, while the other lesions demonstrated stromal PD-L1 staining and infiltration of CD8-positive T cells. PD-1 was positive in lymphocytes from lymph node metastases, but not in those from liver metastases. Data generated using an IO panel indicated higher expression of galectin 9 and higher level of T cell stimulatory checkpoints in lesions with SCLC transformation. Bioinformatic analysis also demonstrated lower expression of type I interferon regulated genes in lesions with SCLC transformation. Conclusion: These data highlight the heterogeneity of expression of immune markers depending on the metastatic sites and histological transformation, and indicate that a biopsy from one lesion may not be representative of immune marker status for all lesions.

Summary of immune marker IHC staining in all specimens

Specimens PD-L1 (tumor) PD-L1 (stroma) TILs CD8 (T cells) PD-1 (T cells) 
Liver metastasis (AC / T790M) 5% 5% ++ negative 
Liver metastasis (SCLC) negative negative scant n.a. n.a. 
Lymph node metastasis (AC / T790M) 5% 5% ++ 
Lymph node metastasis (SCLC) negative 10% ++ 
Specimens PD-L1 (tumor) PD-L1 (stroma) TILs CD8 (T cells) PD-1 (T cells) 
Liver metastasis (AC / T790M) 5% 5% ++ negative 
Liver metastasis (SCLC) negative negative scant n.a. n.a. 
Lymph node metastasis (AC / T790M) 5% 5% ++ 
Lymph node metastasis (SCLC) negative 10% ++ 

Citation Format: Kenichi Suda, Isao Murakami, Hui Yu, Jihye Kim, Kim Ellison, Christopher J. Rivard, Tetsuya Mitsudomi, Fred R. Hirsch. Heterogeneity in immune biomarker expression: Detailed analysis of a case with SCLC transformation after EGFR-TKI treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4583. doi:10.1158/1538-7445.AM2017-4583