Comparison of serum HER2 and CA15–3 in monitoring clinical tumor response in patients with HER2 positive metastatic breast cancer (MBC)

Abstract

9705 Background: HER2 extracellular domain shed from cell surface has been detected in serum (S) of normal individuals and patients (pts) with breast cancer. S HER2 was elevated in >40% of pts with MBC, which was associated with increased tumor volume and poor prognosis. CA15–3 is a conventional tumor marker and elevated in 50–60% of MBC. Therefore, we aimed to compare the S HER2 and CA15–3 in monitoring clinical response to therapy in patients with HER2 positive MBC. Methods: S samples of 37 pts with HER2 positive (measured by immunohistochemistry and fluorescent in situ hybridization) MBC were studied. The serial S HER2 and CA15–3 of 92 samples were measured by immunoassay using Bayer ADVIA Centaur. The correlation of S HER2 and CA15–3 were analyzed, and the changes of both tumor markers were compared with clinical responses (CR, PR, MR, SD, PD). Cutoff value of abnormal S HER2 was ≥15ng/ml and of CA15–3, >38 U/ml. Results: Median age was 46yrs (range 25–66 yrs). ER was positive in 46% and PR, in 27%. HER2 was 3+ in 27, 2+/FISH+ in 7, and 2+ in 4 pts. Twenty six pts received Herceptin mono- or with chemotherapy and 11 pts, other chemotherapy for MBC. S HER2 was elevated in 33 (89%) pts and CA15–3 in 23 (62%) pts prior to therapy. One patient did not show elevation of either marker. Positive correlation between S CA15–3 and HER2 was observed (r = 0.39, p = 0.008). The percent changes of S HER2 and CA15–3 from initial to follow-up according to clinical responses are shown in the Table. Conclusions: Current study suggests that S HER2 is more useful tumor marker than CA15–3 in HER2 positive MBC as it is more often elevated (89% vs 62%), while the variations of both markers during the courses of therapy are well concordant with clinical tumor responses. No significant financial relationships to disclose.