186P - Differences in antigen and immune marker expression in lymphoepithelioma-like carcinoma (LELC) and nasopharyngeal carcinoma (NPC): A multiplex immunohistochemistry (mIHC), spatial transcriptomic and multiplex immunofluorescence (mIF)-based analysis

Background

LELC is an Epstein-Barr Virus (EBV)-associated epithelial tumour histologically indistinguishable from NPC. Due to its rarity, characteristics of pulmonary LELC (PLELC) are poorly understood, and optimal treatment is poorly defined. We report the largest spatial transcriptomic and mIHC/mIF-based comparative analysis of PLELC and NPC, with an aim to characterise their tumour microenvironment (TME), and identify potential prognostic biomarkers and therapeutic targets.

Methods

We examined archival formalin-fixed paraffin embedded (FFPE) PLELC specimens from 39 patients (2000-2019) from National Cancer Centre Singapore and Singapore General Hospital. PLELC samples underwent IHC staining of SSTR2 antibody to assess for SSTR2 expression. Laser capture microdissection (LCM) followed by whole transcriptomic sequencing was also carried out for PLELC samples and compared against NPC datasets, while mIF-based (Vectra 3.0) comparisons were made for NPC and PLELC.

Results

In 20 out of 39 (59%) LELC samples, SSTR2 was positive, with 48% positivity in stage I-III and 75% in stage IV LELC. 59 differentially expressed genes were identified in PLELC compared to NPC (p<0.01) in the tumour epithelial compartment. Preferentially Expressed Antigen of Melanoma (PRAME), a cancer testis antigen with potential for targeting alongside immunotherapy, was particularly highly upregulated (p<0.01). The immune markers CD4, CD8, PD1 and CD137 expression was significantly higher in PLELC, while expression of CD20 was higher in NPC by mIF analyses.

Conclusions

In comparison to NPC, PLELC tumours exhibit an inflammatory TME, with abundant CD4 and CD8 T cells and significantly higher CD137 and PD1 expression. The elevated levels of PRAME, linked to poorer prognosis, along with high expression of both SSTR2 and PRAME in PLELC show promise as potential therapeutic targets.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

National Medical Research Council.

Disclosure

All authors have declared no conflicts of interest.