131 Loss of PD-L1 expression in metastatic Merkel cell carcinoma strongly correlates with a poor prognosis

Abstract

Cutaneous squamous cell carcinoma (cSCC) is the second most common form of non-melanoma skin cancer, causing as many deaths yearly as melanoma in the United States. However, there are limited reliable biomarkers to predict its biological behavior and clinical outcome. The cell division cycle 20 (CDC20) has recently been reported to play a role in cancer progression. But its clinical significance in cSCC has not been studied. The aim of this study was to investigate whether CDC20 was involved in the tumorigenesis of cSCC. We firstly analyzed relative CDC20 mRNA level in two GEO microarray data using GEO2R. In GSE32628, CDC20 mRNA level is significantly higher in precancerous actinic keratoses (AK) (n¼13, p¼0.016) and cSCC (n¼13, p¼0.0007) than the paired normal skin (n¼13). In GSE45216, CDC20 expression was significantly higher in well-differentiated cSCC (n¼15, p¼0.0205), and moderately/poorly differentiated cSCC (n¼15, p¼0.0003) than in AK (n¼10). We then tested the CDC20 expression in 21 paired cSCC and corresponding normal tissues using immunohistochemical staining, and subsequent semiquantitative analysis of the IHC results confirmed increased CDC20 expression in cSCC tissues (n¼21, p < 0.0001). Furthermore, we detected CDC20 expression in 144 samples with different pathological stage. The result showed higher CDC20 in cSCC in situ (n¼27, p < 0.0001), well-differentiated cSCC (n¼29, p < 0.0001), and moderately/poorly differentiated cSCC (n¼25, p < 0.0001) than in normal skin (n¼32) and correlated well with disease progression. CDC20 expression is very low in normal intact skin and is significantly increased in cSCC tumor cells, suggesting it can work as a biomarker for cSCC. Furthermore, elevated expression of CDC20 in both AK and cSCC in situ indicate the induction of CDC20 expression is an early event in cSCC development. However, we didn't have any follow-up data from our patients, so we can't draw any conclusion about the prognosis value of CDC20.