Serum amyloid A: a novel biomarker for endometrial cancer

Abstract

Background: The authors investigated the expression of serum amyloid A (SAA) in endometrial endometrioid carcinoma and evaluated its potential as a serum biomarker.

Methods: SAA gene and protein expression levels were evaluated in endometrial endometrioid carcinoma and normal endometrial tissues, by real-time polymerase chain reaction (PCR), immunohistochemistry (IHC), and flow cytometry. SAA concentration in 194 serum samples from 50 healthy women, 42 women with benign diseases, and 102 patients including 49 grade 1, 38 grade 2, and 15 grade 3 endometrial endometrioid carcinoma was also studied by a sensitive bead-based immunoassay.

Results: SAA gene expression levels were significantly higher in endometrial endometrioid carcinoma when compared with normal endometrial tissues (mean copy number by real-time PCR = 182 vs 1.9; P = .001). IHC revealed diffuse cytoplasmic SAA protein staining in poorly differentiated endometrial endometrioid carcinoma tissues. High intracellular levels of SAA were identified in primary endometrial endometrioid carcinoma cell lines evaluated by flow cytometry, and SAA was found to be actively secreted in vitro. SAA concentrations (microg/mL) had medians of 6.0 in normal healthy women and 6.0 in patients with benign disease (P = .92). In contrast, SAA values in the serum of endometrial endometrioid carcinoma patients had a median of 23.7, significantly higher than those of the healthy group (P = .001) and benign group (P = .001). Patients harboring G3 endometrial endometrioid carcinoma were found to have SAA concentrations significantly higher than those of G1/G2 patients.

Conclusions: SAA is not only a liver-secreted protein, but is also an endometrial endometrioid carcinoma cell product. SAA is expressed and actively secreted by G3 endometrial endometrioid carcinoma, and it is present in high concentration in the serum of endometrial endometrioid carcinoma patients. SAA may represent a novel biomarker for endometrial endometrioid carcinoma to monitor disease recurrence and response to therapy.

Figure 1

SAA mRNA copy number by quantitative RT-PCR in 3 normal endometrial control cell samples (NEC) and 18 EEC snap frozen biopsies. The vertical axis represents the relative number of copies compared to the lowest-expressing NEC (value of 1).

Figure 2

Representative immunohistochemical staining for SAA on NEC paraffin-embedded specimen (A), G1 EEC (B), G2 EEC (C), G3 EEC (D) and G3 EEC-ARK-1 (E), and a liver biopsy (F). NEC 1, G1 EEC and G2 EEC, showed negative staining for SAA while cytoplasmic staining was detectable in representative tissue blocks from both G3 EEC. Strong cytoplasmic SAA positivity was evident in the positive control (i.e., liver). Original magnification 200X and 400X.

Figure 3

A) Serum SAA levels in 50 healthy subjects, 42 benign-disease subjects, and 102 EEC patients. B) Serum SAA levels in EEC with different degrees of differentiation (i.e., 49 G1, 38 G2 and 15 G3 EEC patients). Data are presented as mean ± SEM.

Figure 3

A) Serum SAA levels in 50 healthy subjects, 42 benign-disease subjects, and 102 EEC patients. B) Serum SAA levels in EEC with different degrees of differentiation (i.e., 49 G1, 38 G2 and 15 G3 EEC patients). Data are presented as mean ± SEM.