PARP1 and neoplasm: However, PARP inhibitors also upregulate PD-L1 expression on tumour cells via various mechanisms (e.g., GSK3β, JAK2/STAT3 signalling pathway, or activation of the cGAS-STING pathway) [10–12] which could, in turn, lead to suppression of T-cell-mediated immune responses, and therefore represent a mechanism of resistance to PARP inhibitors [10, 12].