Is parathyroid hormone-related protein a sensitive serum marker in advanced breast cancer?

To compare already used serum markers in advanced breast cancer, namely erythrocyte sedimentation rate (ESR), carcino-embryonic antigen (CEA), and polymorphic epithelial mucins (e.g. CA15-3) with a newer potential marker: parathyroid hormone related protein (PTHrP).

A study group of 33 patients of proven advanced breast cancer was compared with 11 patients with benign breast lumps who were undergoing surgery, and eight patients with humoral hypercalcaemia of malignancy of non-breast origin. ESR, CA15-3, CEA, PTHrP, parathormone (PTH), liver and renal function were measured using commercially available kits. Using given reference ranges, results were classified into normal versus abnormal, and univariate statistical comparisons were made using Fisher's exact test. For multivariate analysis, absolute serum levels were used, and multivariate logistic regression models were employed.

By univariate analysis, only CA15-3 (P = 0.007), and CEA (P = 0.004), were significant markers of metastatic disease. By multivariate analysis the only independently significant serum marker was CA15-3 (P = 0.043). PTHrP was neither a sensitive (22%) nor specific (90.1%) serum marker when compared to CEA or CA15-3. ESR was the most sensitive single serum marker (93%). An incidental finding of elevations of serum parathormone was found in as many patients as in the study group as there were elevations of PTHrP.

PTHrP would not have revealed any patients with metastatic disease that would not have been predicted by any existing tumour markers including CA15-3, CEA and ESR. The finding of elevated PTH in as many patients as PTHrP indicates the possible need for a study inclusive of other polypeptide hormones as markers in advanced breast cancer.