CA15-3: a reliable indicator of metastatic bone disease in breast cancer patients.

Carcinoma of the breast is the most common malignancy in women and is frequently associated with metastatic bone disease and its associated osteolytic morbidity and mortality. Traditional radiological methods for mass screening bony secondaries are not cost-effective. We examined the value of the tumour marker 'CA15-3' as an alternative to conventional isotope bone scintigraphy. A total of 218 patients with breast cancer was evaluated over a 4-year period. Venous CA15-3 levels were obtained at 3-monthly intervals and bone scintigraphy annually or if the patient developed locomotor symptoms or exhibited elevated CA15-3 levels. Of these patients, 33 with metastatic breast carcinoma had an elevated tumour marker level at the time of diagnosis of their metastases; bone metastases alone = 15/17 (88%), soft tissue metastases alone = 2/6 (33%), simultaneous bony and soft tissue metastases = 7/10 (70%). The preponderance of an elevated CA15-3 in metastatic bone disease, be it in isolation or in combination with non-bone metastases, yields a sensitivity, specificity and positive predictive value of 81.5%, 66% and 92%, respectively. Although 22 of the 27 patients had an elevated CA15-3 at the time of diagnosis of their bone metastases, the remaining five patients (with tumour marker levels in the normal range) showed a similar, albeit a delayed, increase (median = 3 months). Thus, all metastatic bone disease patients demonstrated elevated marker levels. We recommend CA15-3 as a simple, reliable and inexpensive screening method for detecting bone metastases in the patient with breast carcinoma.