Human parathyroid hormone-related protein in ovarian small cell carcinoma. An immunohistochemical study

Small cell carcinomas (SCC) are the most common ovarian tumors associated with hypercalcemia. Parathyroid hormone-related protein (PTHrp) is the most frequent cause of hypercalcemia of malignancy.

The presence of PTHrp in SCC has been studied by immunohistochemistry in formalin fixed, paraffin embedded tissues. A polyclonal antibody against a synthetic peptide corresponding to the first 36-N terminal amino acid residues of PTHrp was used. Normal dog skin, which is rich in PTHrp, was used as a positive control. Absorption tests using the synthetic peptide as antigen were done in all the cases.

Immunoreactivity for PTHrp was found in five of seven cases of SCC. The serum calcium levels were elevated in two of these cases, normal in two, and unknown in one. The two negative cases were associated with high serum calcium levels.

The lack of correlation between immunoreactivity and serum calcium levels can be explained on the basis that immunohistochemistry is dependent on the peptide content of cells rather than on the capability for hormone production and/or release. The results suggest that PTHrp plays a role in the development of hypercalcemia in patients with SCC of the ovary.