Serum bone alkaline phosphatase and CA 549 in breast cancer with bone metastases

A monoclonal radioimmunometric assay for bone alkaline phosphatase (BAP) developed by Hybritech, USA, with an upper limit of normal of 40 U/l, was examined in 125 patients with breast cancer. Eleven patients who remained tumour free for 5-6 years had small intra-individual variations of BAP. The median value in 33 patients with multiple bone metastases of 60 U/l was elevated when compared with that in 40 patients with no evidence of metastases (22 U/l) and 34 U/l in 16 with limited bone disease (1-2 hot spots). By contrast, only 2 out of 25 patients with extensive local recurrence, lung, or hepatic metastases, without bone involvement showed an increase of BAP (< 200 U/l). The BAP levels were compared to total alkaline phosphatase (TAP), the breast cancer marker CA 549 (HybriBREScan). Longitudinal studies of 15 patients with bony metastases showed that TAP and BAP were well correlated only when the TAP was elevated; CA 549 and BAP could vary independently. The main use of BAP in patients with bone metastases appears to be an aid to the monitoring of treatment; however, it is not significantly raised in limited bone metastases.