Oral 1.03: Frequent PD-L1 expression in thymic squamous cell carcinoma of Chinese patients

Background: A recent publication reported diffuse high intensity PD-L1 staining in thymic epithelial tumor (TET). The PD-L1 scores and histology were significantly correlated, with higher intensity staining in WHO classification B2/B3/C TET. Among B2/B3/C TET, thymic squamous cell carcinoma (TSQCC) has morphological features of squamous cell carcinoma as seen in other organs. Unlike thymomas, it generally lacks resemblance to the normal thymic cytoarchitecture. Here we examine PD-L1 expression in a TSQCC of Chinese patients.

Methods: Fifteen TSQCC specimens obtained from the Shanghai Chest Hospital tissue archive were stained with Merck Serono anti-PD-L1 antibody MKP1A07310 on Ventana’s (instead of Dako) core reagent and instrumentation platform. Scoring of PD-L1 expression on a semi-quantitative scale was performed by a trained surgical pathologist, who is blinded to clinical data and sample identity. The percentage of tumor cells expressing membrane PD-L1 immuno-reactivity at the intensities weak (1+), moderate (2+), and strong (3+) will be recorded.

Results: Strong PD-L1 expression was observed in five specimens (30%). A focal (instead of diffuse) staining pattern on tumor cell membrane (instead of both membrane and cytosol) was observed. The medial age with positive expression of TSQCC was 61 years old, and 60% was male. Tumour stage at strong PD-L1 positive was IIA, III, IV respectively in 20%, and stage IIB in 40%.

Conclusions: PD-L1expression was present in TSQCC. Strong expression was observed in 30%. The correlation of the clinic-pathological parameters and PD-L1 expression in TSQCC should be research.

Keywords: PD-L1; thymic tumor; histology