Tumour marker CA15-3: possible uses in the routine management of breast cancer.

Tumour markers are a potentially powerful means of obtaining information about cancers whilst causing minimal morbidity, inconvenience and cost. CA15-3 has been suggested as a marker of distant metastasis (M+ disease) in breast cancer. We have measured CA15-3 in 77 patients with carcinoma of the breast in order to determine whether routine assay of this tumour marker would be useful in the oncology unit of a district general hospital. A highly significant correlation existed between elevated CA15-3 levels (> or = 30 U/ml) and M+ disease. The CA15-3 assay was found to have a sensitivity of 70%, a specificity of 96% and a predictive value of 87%, in agreement with previous studies. There was evidence that CA15-3 levels frequently increased in advance of otherwise detectable distant metastases. 70 patients had a 99m Tc bone scan close to the date on which CA15-3 was measured. All patients with a positive bone scan and raised levels of CA15-3 were subsequently confirmed as having bony metastases; no patient with normal bone scan and normal CA15-3 developed M+ disease (to the date of follow-up). CA15-3 levels were raised in 83% of patients who developed non-bony distant metastases. In clinical practice it may be possible to exploit the high specificity of CA15-3, in order to provide additional information to that already determined by current investigations. For example, CA15-3 might be assayed alongside a bone scan to confirm positive or negative results. Another role might be as a screen for breast cancer metastases in departments with limited access to bone scans and other imaging facilities. CA15-3 might also be used in monitoring patients for the development of distant metastases during follow-up. It is, however, unlikely that CA15-3 can substitute directly for a bone scan or other imaging currently used routinely by a department. Clinical trials are now necessary to determine the effect of using tumour markers such as CA15-3 on patient morbidity and mortality.