Detection of secondary metastatic breast cancer by measurement of plasma CA 15.3

BACKGROUND: Most current guidelines do not recommend the serial analysis of tumour marker CA 15.3 in the follow-up of asymptomatic patients treated for early breast cancer (EBC). These guidelines are based on small-scale studies carried out in an era with more limited treatment options than today. In our large academic centre, serial measurements of CA 15.3 are used routinely in the follow-up of EBC, whereas imaging for distant metastases is only carried out on indication. PATIENTS AND METHODS: In this retrospective single-centre study, patients were included if they were treated for EBC between 1 January 2000 and 1 January 2018, diagnosed with secondary metastatic disease at least 6 months after initial surgery and had CA 15.3 available at the time of diagnosis of metastases. The primary objective was to evaluate the proportion of patients in whom metastatic disease was discovered by an increasing CA 15.3. Information on the method of metastases detection, CA 15.3 evolution and survival was collected after approval of the ethics committee. RESULTS: At the moment of diagnosis of metastases, 451 of 730 included patients (62%) had CA 15.3 levels above the upper limit of normal (>30 kU/l). In 269 patients (37%), an increasing CA 15.3 was the first sign that led to the diagnosis of metastases. This was most frequent in luminal A-like tumours (48%) and in liver (45%) and bone (41%) localisation of metastases. By contrast, reported symptoms triggered the diagnosis of metastatic disease in 48% of the patients. Median overall survival was significantly longer when the relapse was discovered by CA 15.3 elevation versus those discovered by another trigger (abnormal clinical examination or history, abnormal laboratory tests or an incidental finding) (35 versus 22 months; P = 0.0027). CONCLUSION: When CA 15.3 is systematically used in the follow-up of EBC patients, the diagnosis of metastatic disease is made in 37% by a CA 15.3 increase.