THE EXPRESSION OF PARATHYROID HORMONE-RELATED PROTEIN IN HUMAN BREAST-CANCER WITH SKELETAL METASTASES

The relationship between the expression of parathyroid hormone-related protein (PTHrP) by breast cancer and skeletal metastases, was investi gated using a monoclonal antibody against human PTHrP (4B3). The immun ohistochemical localization of PTHrP was studied in sections of formal in-fixed, paraffin-embeded tissues from 28 breast cancers obtained sur gically between 1980 and 1985. Of the 28 patients, 12 developed skelet al metastases, 8 developed lung metastases, and the other 8 were alive and disease-free at the time of this study. Sixteen of the 28 (57%) t umors showed positive immunoreactivity to 4B3, the PTHrP positive rati o being 83% in the patients who developed skeletal metastases, 38% in those who developed lung metastases, and 38% in those without recurren ce, respectively. Thus, a significantly higher proportion of the patie nts who developed skeletal metastases were positive for PTHrP than the other two groups (P < 0.05). Furthermore, the level of positive stain ing was strongly related to positivity for estrogen and progesterone r eceptors (P < 0.01). These results are consistent with the hypothesis that PTHrP might be necessary for metastases to erode bone and grow in skeletal sites, and its expression could be related to certain hormon es.