The concentration of 67Ga and 45Ca in the lactating mammary gland and its relevance to the tumor uptake of 67Ga citrate.

67Ga is known to concentrate in the breasts of pregnant and postpartum women, and a case is now described in which 67Ga uptake was seen in the breasts of a woman who was neither pregnant nor postpartum, but was receiving chemotherapy for Hodgkin's disease. Comparative studies of the uptake of 67Ga and 45Ca in lactating dogs have shown that both nuclides are secreted in the milk in similar amounts and in protein-bound form. The concentration of 67Ga in mammary tissue is about one-half of that found in the milk at 5 hr postinjection but, by 48 hr, the concentrations are approximately equal. There were similarities in the subcellular distributions of 67Ga and 45Ca in the lactating mammary gland at 5 and 48 hr. Although there was a correlation between 67Ga and 45Ca in individual pieces of a lactating mammary gland at 5 hr after injection, no such correlation was seen between the two nuclides in multiple samples of a transmissible venereal tumor measured at various time intervals. The rate of dispersion of 67Ga and 45Ca from the lactating mammary gland was similar but, in the tumor, 67Ga was present in very much greater amounts than 45Ca and was retained longer. It is concluded that, although there may be similarities in the metabolic pathways of gallium and calcium in the lactating mammary gland, there is no similarity in the mechanism of uptake of these two elements into tumors.