Parathyroid hormone–related protein and hypercalcemia secondary to massive mammary hyperplasia

To the Editor: Parathyroid hormone-related protein (PTHRP) is a recently characterized 141-amino acid peptide that is responsible for the humoral hypercalcemia of cancer.¹ We previously reported on a patient with massive mammary hyperplasia occurring during pregnancy who had hypercalcemia that resolved after bilateral mastectomy.² Recent studies done on tissue from this patient implicate PTHRP as the likely etiologic factor in her hypercalcemia. The patient was a 25-year-old woman who presented with bilateral breast enlargement of two months' duration. She was 24 weeks pregnant at that time. She had had two uneventful earlier pregnancies and had never had nonpuerperal galactorrhea. She.