CA 15-3 (also known as MUC1) is the most widely used serum marker in breast cancer. MUC1 is a large transmembrane glycoprotein which is frequently overexpressed and aberrantly glycosylated in cancer. Physiologically, MUC1 appears to play a role in cell adhesion and the high levels present in cancer may be causally involved in metastasis. At present the main uses of CA 15-3 are in preclinically detecting recurrent breast cancer and monitoring the treatment of patients with advanced breast cancer. In a prospective study of 368 patients we show that patients with high preoperative levels of CA 15-3 (>30.4 U/mL) had a worse outcome than patients with low levels of the marker. In multivariate analysis CA 15-3 as a prognostic marker was independent of both tumor size and nodal status. Furthermore, in multivariate analysis the prognostic impact of CA 15-3 was stronger than that of tumor size and at least as strong as nodal status. CA 15-3 may thus be the first independent prognostic serum marker in breast cancer.
Background. The value of circulating CA 15‐3 levels was assessed in 129 patients with recurrent breast carcinoma.
Methods. Patients were divided into four subgroups, according to the following: Group A, locoregional recurrence alone; Group B, locoregional and subsequent systemic recurrence; Group C, combined locoregional and systemic recurrence; and Group D, differing sites of systemic disease.
Results. One of 14 patients with locoregional disease alone had increased levels of CA 15‐3 (> 25 U/ml). However, 96% of patients (22 of 23 patients) with combined local and systemic disease had increased tumor marker levels. The difference in CA 15‐3 levels in patients with combined disease compared with patients with local disease alone was statistically significant (117.0 versus 17.5 U/ml, respectively; P < 0.02). Twenty‐four patients with locoregional recurrence later had distant metastasis develop. In this group, patients with an increased CA 15‐3 value had a significantly shorter lead time to the development of distant metastases compared with patients with normal tumor marker levels (20.8 ± 3.3 versus 10.3 k 2.7 months, respectively; P < 0.03). CA 15‐3 values at diagnosis were increased in 88% of 115 patients with metastatic disease. There was no significant difference in CA 15‐3 levels among metastases to lung, liver, and bone nor was there any difference between single and multiple sites of distant metastasis. CA 15‐3 is an excellent marker for systemic recurrence of breast carcinoma.
Conclusions. Increased levels and no clinical evidence of recurrence strongly indicate the presence of occult metastatic disease.
Preoperative serum concentrations of CA 15-3 appear to have a significant relation to outcome in patients with early breast carcinoma and may have a role in the rational selection of patients for appropriate adjuvant treatments. To the authors' knowledge, CA 15-3 thus is one of the first circulating markers shown to be an independent prognostic indicator in patients with breast carcinoma.
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