Plasma levels of a viral protein as a diagnostic signal for the presence of tumor : the murine mammary tumor model.

We used the mouse mammary tumor and its associated virus (murine mammary tumor virus) to examine the possibility of using plasma levels of a viral protein (gp52, the glycoprotein of 52,000 molecular weight) as a diagnostic indicator of the presence of a solid tumor. The following features have emerged from our studies: (a) tumor-bearing animals show markedly elevated (100-1000 ng/ml) plasma levels of gp52 and the mean concentration increases with tumor size; (b) mammary tumor tissues located outside the mammary gland are also detected by the elevated plasma gp52; (c) low (2-10 ng/ml) plasma levels of gp52 are found in tumor-free mice, whether they are derived from strains characterized by high or low frequencies of spontaneous mammary tumors; (d) tumor-free lactating females exhibit the normally low levels of plasma gp52 despite the fact that their milk contains an average of 20,000 ng/ml of this antigen; (e) thus, high levels of plasma gp52 are found only in the presence of tumor and are not induced by either predisposition for the disease or by normal production of the antigen during lactation; (f) the circulatory clearance time of gp52 is sufficiently rapid to require continued replenishment to maintain the high levels observed in tumor-bearing animals, a feature implying that the gp52 concentration can be a responsive parameter of disease status. The information obtained suggests that plasma gp52 is a potentially useful and specific systemic indicator of the presence and extent of murine mammary neoplasia.