PARATHYROID HORMONE-RELATED PROTEIN IN PATIENTS WITH PRIMARY BREAST-CANCER AND EUCALCEMIA

Parathyroid hormone-related protein (PTHrP) is a causative factor of h umoral hypercalcemia in breast cancer and other malignancies. We studi ed circulating PTHrP levels with three different immunoassays directed against different parts of the PTHrP molecule in 48 patients with bre ast cancer and eucalcemia. The methods used were: (a) a RIA with antib odies directed toward the midregion (63-78); (b) an immunofluorometric assay with two antibodies against 1-34 and 38-67; and (c) an immunora diometric assay with antibodies against 1-40 and 1-72. Although most p atients had PTHrP levels indistinguishable from normal when measured b y all three methods, four patients had increased serum levels in the I FMA. PTHrP was detected by immunohistochemistry in tumors from nearly all patients. One patient,vith elevated PTHrP in plasma measured by IF MA showed intense staining of tumor by immunohistochemistry; the tumor was histologically graded as III (severe) and was the largest of all tumors in this patient group. The IFMA can identify increased serum PT HrP in some patients with breast cancer who are not hypercalcemic, Thi s assay may be especially useful in screening patients for this tumor during a relative early phase of the disease.