P5-13-18: A Study of the Usefulness of Tumor Markers CA 15–3 and TPS in Monitoring of Different Subgroups of Metastatic Breast Cancer.

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Abstract Background: The sensitivity and specificity of the tumor markers cancerantigen 15–3 (CA15-3) and the more seldom used tissue polypeptide specific antigen (TPS) for detecting and monitoring metastatic breast cancer are relatively well known. However, most of the studies in this area were performed before the era of breast cancer subtyping and some recent reports have showed differences in the sensitivity of CA 15–3 among different subtypes of breast cancer. This implies that the usefulness of a tumor marker could vary among different subgroups. We performed a retrospective study to find out the usefulness of CA 15–3 and TPS in long-term monitoring of metastatic breast cancer subgrouped by hormonal and HER2−receptor status. Patients and methods: CA 15–3 was routinely assessed regularly in all patients with metastatic breast cancer since 2003, while TPS was assessed during years 2005 — 2009. In total 142 patients (median age 60 years, range 22–87) with metastatic breast cancer were identified in the local data base and included. The total number of analyzed CA 15–3 samples were 4232 (mean 30/patient) and TPS 1993 (mean 14/patient). In each patient the results of the markers were compared with disease response and progression during different lines of therapy and the patients were grouped based on the ratio of correct tumor marker values: “1” (useless) if 0–49% of the values were regarded as true, “2” (poor) if 50–74% were true, “3” (good) if 75–94% were true and finally “4” (excellent) if 95–100% of the values were considered true. If a patient had no elevated values during follow-up, she was reported as tumor marker negative: “0”. Results: In general, the usefulness of CA 15–3 was excellent (4) in 50% of patients and good (3) in 16% more, compared with only 12% and 23% for TPS. Twenty-three percent and 25%, respectively were marker negative (0). There was a marked difference in the different subgroups. CA 15–3 was very useful (group 3 + 4) in estrogen and progesterone receptor positive patients (79%) and hormonal positive HER2 positive patients (82%), compared with only 40% in the triple negative group and 27% of the patients in the hormonal negative HER2 positive group. TPS showed the opposite tendency with less value in hormonal positive patients (only 31% in group 3 and 4) compared with 40% in triple negative and 45% the hormonal negative HER2 positive group. Other factors with strong positive influence of the value of the marker were high absolute values, increased value at diagnosis of metastatic disease (initial value) and visceral metastases. Conclusion: Metastatic breast cancer can be well monitored using CA 15–3 in about 80% of the cases if the tumor is estrogen or progesterone positive. Hormonal receptor negative disease may be well monitored with CA 15–3 and/or TPS if there are elevated initial values, high absolute values and visceral disease. HER2−status seems not to influence the usefulness of CA 15–3 and TPS. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-13-18.