Abstract P4-01-17: Expression of circulating tumor cells (CTC) and CK-19 mRNA (CK19) as prognostic factors in heavily pretreated metastatic breast cancer

Abstract Introduction: The expression of CTC and CK19 holds prognostic value for patients with breast cancer but their clinical significance remains still controversial. Methods: This clinical observational study included 58 preteated metastatic breast cancer patients who started a standard new treatment line. CTC and CK19 was measured with CellSearch® and RT-PCR respectively at inclusion time. Progression-free survival (PFS) was defined as the time elapsed between the initiation of the treatment and either the date of clinical or radiological progression or death or the last follow-up. Cox proportional hazards regression model was used to assess the univariate prognose value of CTC and CK19 on PFS, and Kaplan-Meier estimates. A multivariate Cox model was also performed to additionaly account for ER and visceral disease. CTC and CK19 positivity was considered when a value of 1 or more was observed. Results: Mean age was 59.68 (range 35-86), the average number of previous treatments was 2.98 (range 1-10), 38 patients (65.52%) were ER+ and 22 (37.93%) had visceral disease. Median PFS was 7 months (CI 95% 4-9). Univariate analyses showed a significant effect of the positivity of CK19 (HR=2.22, CI 95% 1.15-4.29, p=0.01) but did not reach statistical significance for CTC (HR=1.86, CI 95% 0.93-3.72, p=0.07). The estimate disease-free survival rate at 6 and 12 months were 63.6% and 43.4% for patients with CK19<1 and 47.1% and 10.6% for patients with CK19>=1, respectively. The estimate disease-free survival rate at 6 and 12 months were 77.8% and 28.8% for patients with CTC=0 and 43.6% and 21.5% for patients with CTC>=1, respectively. In the multivariate analysis the effect of CK19 and CTC were similar (HR=2.12 and 1.86, p=0.03 and 0.08 respectively), ER was statistically significant (HR=0.48, p=0.05, + vs -) but visceral diseases appeared not significant (HR=1.57, p=0.17, yes vs no). Conclusions: The expression of CK19 appeared clinically meaningful in pretreated metastatic breast cancer patients, even when adjusting by ER and visceral diseases. CTC showed a similar but minor effect and not statistically significant. These results support CK19 as an interesting biomarker for predicting clinical response in metastatic breast cancer. Citation Format: Serafin Morales, Ana Velasco, Jose Vidal, Anna Serrate, Joan Valls, Juan Carlos Samame, Rafael Gisbert, Desamparados Moral, Antonio Llombart, Antonieta Salud, Xavier Matias-Guiu. Expression of circulating tumor cells (CTC) and CK-19 mRNA (CK19) as prognostic factors in heavily pretreated metastatic breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P4-01-17.