CALCA and small cell lung carcinoma: The intracellular precursor of calcitonin, currently known as procalcitonin (PCT), was first discovered in 1975 during the study of calcitonin biosynthesis in chicken ultimo-branchial glands.6 In 1981, a similar molecule was discovered in human thyroid medullary carcinoma tissue leading to the description of the exact structure of PCT.7 The level of PCT in healthy individuals is much lower than the detection threshold and was only known to increase in patients with medullary thyroid and small cell lung carcinoma.