GRP and neoplasm: SCLC is a neuroendocrine cancer that secretes a range of neuropeptides which act, through autocrine and paracrine loops, as growth factors to stimulate and sustain the proliferation of tumour cells.8–10 Among these are the calcium-mobilising neuropeptides, such as the gastrin-releasing peptide (GRP), bradykinin, cholecystokinin, neurotensin and vasopressin.