Placenta specific 1: a novel marker for detection of metastasis in mouse model of breast cancer.

Background: Placental-specific 1 (Plac1), with no expression in normal tissues, is expressed in different cancers. Therefore, the potential application of Plac1 to detect metastasis was investigated in breast cancer model.

Methods: A spontaneous metastasis model was established using 4T1 cells. FDG-PET and histological analysis were used to detect metastasis. Plac1 expression was assessed in a wide range of tumor-bearing and normal mice tissues by RT-qPCR. The sensitivity of Plac1-positive cell detection was examined by 4T1 serial dilution in Plac1-negative cells.

Results: Plac1 was not expressed in normal mouse tissues (n = 6), except in the brain (6/6, dCT = -10.85). 4T1 cell line (dCT = 0.65) and 4T1-induced tumor (dCT = -0.29) were positive for Plac1 expression. PET imaging and histopathology analysis demonstrated metastases in the lung, liver, and spleen of tumor-bearing mice. Plac1 expression was confirmed in lung (6/6, dCT = -1.52), liver (6/6, dCT = -2.37), spleen (6/6, dCT = -3.7), kidney (2/6, dCT = -40.00), brain (6/6, dCT = -7.47), and blood (6/6, dCT = -3.35) of tumor-bearing mice. The sensitivity of detecting tumor cells is at least one cell per million cells.

Conclusions: Plac1 is a novel marker with high specificity and sensitivity for detecting metastasis in breast cancer. These findings provide a rationale for human studies.