Plasma Levels of a Viral Protein during Adjuvant Treatment: Reflection of Murine Mammary Tumor Status and Therapeutic Effect

The mouse mammary tumor and its associated virus, mouse mammary tumor virus, were chosen to test the possibility of using plasma levels of a M r 52,000 viral glycoprotein (gp52) as a means for monitoring changes in tumor status during surgical adjuvant cyclophosphamide:doxorubicin (Adriamycin):5-fluorouracil treatment. Analysis of tumor recurrence and plasma gp52 concentrations during the postoperative period demonstrated that both parameters were significantly decreased in the group receiving cyclophosphamide:doxorubicin:5-fluorouracil treatment. This observation suggests that plasma gp52 levels may be a useful alternative measure of therapeutic effect during surgical adjuvant treatment. A retrospective analysis of gp52 plasma levels and tumor status of individuals during treatment has revealed the following associations. ( a ) An early sharp postsurgical elevation in plasma gp52 level was associated with subsequent death of treated animals. ( b ) Maintenance of postsurgical gp52 levels at a low level (≤4.2 ng/ml) during and after treatment was characteristic of all tumor-free survivors. ( c ) A gradual rise in plasma gp52 level accompanied CAF-delayed tumor recurrence. gp52 levels increased in all treated animals 2 wk prior to detectable tumor regrowths, resulting in a statistically significant increase in mean gp52 level (2.2 to 5.4 ng/ml). However, the magnitude of this increase was small for the majority of animals with tumor regrowths, and greater, more definitive elevations in plasma gp52 levels were only detected at the time of frank tumor recurrence. In addition, comparisons of early mean gp52 levels (8 to 10 days after surgery) for controls and for animals receiving various forms of alternative treatment have indicated that differences in gp52 levels reflect subsequent differences in recurrence rates. The present data, obtained during surgical adjuvant treatment of BALB/c × DBA/8 F1 mice and viewed in a retrospective fashion, demonstrate that plasma gp52 concentrations reflected therapeutic effects.