Elevated serum calcium concentrations in mammary tumor bearing C3H/Fg mice without bony metastases.

Sera from eight adult C3H/Fg mice bearing spontaneous mammary gland tumors were analyzed for calcium content in two successive weekly samples. The sera from six mice were fount to have significantly elevated serum calcium concentrations while sera from two were normocalcemic. Intramuscular implantation of mammary gland tumors into 12, 3-month-old female C3H/Fg mice resulted in significant and progressive increases in serum calcium concentrations over a 4-week period. Subcutaneous implants had a similar effect, but gave less consistent results. These data supported the hypothesis that mammary gland tumors are capable of inducing elevated serum calcium concentrations in C3H/Fg mice. It was concluded that low grade elevation of serum calcium occasionally seen in adult female C3H/Fg mice may be caused by incipient mammary gland tumors.