CXCR4 and cholangiocarcinoma: The most promising applications in solid tumours appear to be theranostic approaches to the treatment of refractory advanced cholangiocarcinoma, adrenocortical carcinoma, vestibular schwannoma, small cell lung cancer, oesophageal cancer and high-grade neuroendocrine tumours, to select patients likely to benefit from therapies targeting CXCR4 including targeted radionuclide therapies with 177Lu- and 90Y-Pentixather in combination with stem cell transplantation in a selected group of patients with no other therapeutic options.