Association of serum levels of the growth factor GP88 with disease progression in breast cancer patients

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Background: The autocrine growth factor GP88 is an important player in breast cancer. GP88 is expressed in human BC tumors in correlation with their tumorigenicity. Increased GP88 expression was associated with anti-estrogen therapy resistance in ER+ cells and Herceptin resistance in Her-2 overexpressing breast tumors. Inhibition of GP88 expression inhibited tumor incidence and growth in nude mice. Immunohistochemical studies have shown that GP88 is expressed in invasive ductal carcinomas (IDC) and that high GP88 expression correlated with increased recurrence and mortality. Since GP88 is found in serum, we hypothesized that GP88 was elevated in the sera of breast cancer patients compared to healthy individuals and that GP88 serum level increases with disease progression. Methods: An IRB approved prospective study was established at the University of Maryland Breast Clinic to determine the serum level of GP88 in breast cancer patients (BC pts). Approximately 5 ml of blood was drawn every three months. GP88 serum concentration was determined in triplicate by human GP88 enzyme immunoassay. 190 BC pts were accrued. Sera from healthy volunteers (HV) were obtained to establish GP88 baseline. BC patient characteristics: Caucasian- 91, African American-92, Asian-6; median age, 51 (range 29- 86), stage I - 48, II - 52, III - 26, IV - 63. Results: Median serum GP88 level was 28.7 ng/ml (range 16.6–38.2) in HV, 40.7 ng/ml (range 6.4–100) in early stage (stage 1 -3) BC pts (p- value = 0.007) and 45.3 ng/ml (range 9.8 to 158.4) in stage 4 BC patients (p- value= 0.0007). Statistically significant increase in serum GP88 level was found in early stages as well as in metastatic disease when compared to HV. In addition, patients that were initially diagnosed with early stage disease but recurred showed a 5 to 10 fold increase in their GP88 serum levels. Conclusions: GP88 serum level is significantly higher in the sera of BC than HV subjects. Moreover, GP88 serum level increased in association with disease recurrence and progression. This study identifies GP88 as a measurable biomarker for disease progression not only at the tissue but also at the serum level. These results are also interesting since GP88 is also a therapeutic target of malignant progression of breast carcinoma.

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Elevated serum levels of the growth factor GP88 are found in breast cancer patients when compared to healthy individuals

Abstract #2006

Background: GP88 is an autocrine growth factor that plays a critical role in breast tumorigenesis. GP88 is expressed in human BC tumors in a positive correlation with their tumorigenicity. Increased GP88 expression is associated with resistance to anti-estrogen therapy in ER + cells and with herceptin resistance in Her-2 overexpressing breast tumors. Inhibition of GP88 expression in human breast adenocarcinoma inhibited tumor incidence and growth in nude mice. Immunohistochemical studies have shown that GP88 was expressed in invasive ductal carcinomas in correlation with the expression of poor prognosis markers whereas normal tissues and benign lesions were negative. High GP88 expression in tumor biopsies was accompanied by decreased disease-free survival. Since GP88 can be secreted, we have hypothesized that GP88 could be secreted in the circulation and found in serum. We examined whether GP88 could be found in the circulation and whether GP88 could be elevated in the sera of breast cancer patients when compared to healthy individuals.
 Methods: An IRB approved blood sampling study was conducted at the University of Maryland Breast Clinic to determine the serum level of GP88 in healthy volunteers (HV) and breast cancer patients (BC pts). Serum GP88 concentration was determined in triplicate by quantitative enzyme immunoassay. 189 BC pts were accrued. In addition, sera from 18 HV were obtained to establish a GP88 baseline in healthy volunteers. BC patient characteristics: Race: Caucasian- 91, African American-92, Asian-6; median age, 51 (range 29-86), stage I – 48, II - 52, III – 26, IV - 63.
 Results: Circulating GP88 was measurable in the serum. Median level of GP88 was 28.7 ng/ml (range 16.6-38.2) in HV; 40.7 ng/ml (range 6.4-100) in early stage (stage 1 –3) BC pts (p- value = 0.007) and 45.3 ng/ml (range 9.8 to 158.4) in stage 4 metastatic BC patients (p-value= 0.0007). Statistically significant increase in circulating GP88 level was found in early stages as well as in metastatic disease. Correlation studies with BC prognostic factors such as stage, tumor size, lymph node involvement, tumor grade and presence of ER and HER-2 will be presented.
 Conclusion: GP88 can be detected in the sera of HV and BC pts. Comparison between the two groups of subjects indicates that GP88 level is significantly higher in the sera of BC pts. These studies are important as they identify as a measurable circulating biomarker GP88 that is also a therapeutic target of malignant transformation or malignant progression of breast carcinoma (BC). Future studies will examine whether there is any correlation between the serum level of GP88 and therapeutic response to systemic therapy in breast cancer patients.
 This study was supported by grant from MIPS, the Avon Foundation and 1R43 CA 124179-01A1 from the National Institutes of Health.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2006.