Significance of serum tumor markers in monitoring advanced breast cancer patients treated with systemic therapy: a prospective study.

OBJECTIVE: The significance of serum tumor markers in monitoring advanced breast cancer patients is still controversial. To clarify this issue, the Tumor Marker Study Group of the Japanese Breast Cancer Society conducted a prospective study.
METHODS: Patients with advanced breast cancer who were treated with systemic therapy between January and December 2002 were recruited from five collaborative institutes in Japan. The patients were monitored every four weeks using three serum tumor markers, CEA, CA 15-3 and NCC-ST-439 during the therapy.
RESULTS: Findings from 108 eligible patients were analyzed. The pretreatment positivity rates were 51.9% for CEA, 50% for CA 15-3, and 34.3% for NCC-ST-439. The changes in each marker level at 8 and 12 weeks but not at 4 weeks after the start of therapy seemed to correlate with the response to therapy in pretreatment marker-positive patients but not in negative patients. The Cox proportional hazard model revealed a greater than 20% reduction in CEA, CA 15-3 or NCC-ST-439 levels at 4, 8 and/or 12 weeks after the start of therapy to be an independent predictive factor for longer time-to-progression (TTP) in pretreatment marker-positive patients.
CONCLUSION: This prospective study supported the findings obtained from our previous retrospective study that in pretreatment marker-positive patients 1) the changes in serum tumor marker levels after the start of therapy correlate with the response to therapy; and 2) a greater than 20% reduction in the tumor marker levels was a favorable predictive factor for TTP during systemic therapy. When the pretreatment serum level of these markers is over the respective cut-off value, sequential measurement of them may be useful for evaluating the efficacy of treatment as well as monitoring the outcome of patients with advanced breast cancer.