PDCD1 and hepatocellular carcinoma: ROBO1 in clinical HCC samples is significantly and positively correlated with multiple ICIs, including cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), Programmed cell death protein 1 (PD-1), CD274, T-cell immunoreceptor with Ig and ITIM domains (TIGIT), and butyrophilin subfamily 2 member A1 (BTN2A1) and BTN2A2 [69].