AKT-4586

A 75-year-old man presents with weight loss and is found to have a serum calcium concentration of 3.22 mmol/l (normal range 2.25-2.5 mmol/l). A skeletal survey is normal. A cancer with non-metastatic hypercalcaemia is suspected.
Which of the following substances is most likely to be secreted by the tumour in this case?