Variability of Mouse Mammary Hyperplastic Nodules Maintained in Organotypic Culture

Summary

Although most hyperplastic alveolar nodules from the mammary glands of female C3H/Crgl mice are morphologically homogeneous, the amounts of secretion and of fibrous connective tissue vary. To determine the extent of variation in the capacity of nodules to survive in vitro without hormones, nodules were placed in organ culture for 6, 9,12, and 15 days. After culture, the alveolar structure of the nodules had largely disappeared, though some parenchymal cells still seemed viable. To demonstrate their viability, cultured expiants were transplanted into mammary fat pads cleared of their normal parenchyma. Outgrowths were produced by 63% of the transplanted expiants. Prolongation of time in culture did not appreciably affect the frequency of outgrowths obtained from nodules. The histology of outgrowths was variable, even when they originated from different parts of a single, cultured nodule. Some nodular outgrowths were densely infiltrated by lymphocytes; others were distinguished by acidophilic cytoplasmic inclusion bodies (presumably masses of virus). About 50% of the outgrowths from cultured nodules produced tumors within 6 months; prolongation of the culture period had no appreciable effect on the frequency of tumor formation. The results provide evidence that mammary nodules, despite considerable gross morphological uniformity, are highly variable in their responses to organ culture and to subsequent transplantation.