Date of Award


Degree Type


Degree Name

Master of Science (Medical Science)


School of Medical and Health Sciences

First Advisor

Associate Professor Elin Gray

Second Advisor

Professor Melanie Ziman


Incidence rates for both melanoma and non-small cell lung cancer (NSCLC) have risen in recent decades. While advanced cases of both diseases have previously demonstrated low survivability, novel therapies such as immune checkpoint inhibitors, have significantly improved the outcome of patients suffering from these cancers. Recent clinical trials have led to the United States Food and Drug Administration (FDA) approving the use of antibodies targeting the PD-1 immune checkpoint for both melanoma and NSCLC. Anti-PD-1 antibodies have been seen to illicit responses in up to 40% of patients, however, particularly for melanoma, there is a lack of biomarkers to select for patients likely to respond.

PD-L1 expression in tumour tissue is the most studied biomarker of response to anti-PD-1 therapy in melanoma patients and is also the biomarker currently in use as a companion diagnostic test for NSCLC patients. It is believed that circulating tumour cells (CTCs) that break away from the tumour and enter the bloodstream, would share the same immune escape mechanisms as the parent tumour, and so would express PD-L1 in the same way as the tumour. Therefore, we postulate that these cells provide an accessible tumour sample for analysis of PD-L1 expression.

A previous study by our group used multi-marker flow cytometry to evaluated PD-L1 expression on CTCs from melanoma patients commencing anti-PD-L1 therapy. Here, the PDL1 expression on CTC from the latter study was compared to PD-L1 expression in matched tumour tissues. Moreover, this study describes the establishment of methodologies for immunocytochemistry analysis and scoring of PD-L1 expression on melanoma CTCs and on carcinomas CTCs, including NSCLC. Cell lines representing negative, low and high PD-L1 expression were identified to serve as controls, again for both melanoma and carcinomas. To further evaluate our methods, CTCs were extracted from the blood samples of patients with melanoma and NSCLC using microfluidic devices and immunostained to investigate the expression of PD-L1. Finally, comparison between CTC and tumour tissue PD-L1 expression was carried out in a small number of cases.

Overall, this study successfully developed immunocytochemistry protocols to effectively identify and score PD-L1 expression on both melanoma and carcinoma CTCs, thus providing a basis for further work to evaluate the clinical potential of CTCs.