Identification of malignant cells in primary monolayer cultures of human breast tumors.

Primary monolayer cultures of human breast tumors have been characterized by using light microscopy on cultures incubated for glucose-6-phosphate dehydrogenase (G6PDH) activity. The enzyme activity was compared with that of the corresponding histological sections as well as with that of three established human cell lines. Furthermore, electron microscopy has been carried out on selected, isolated cell islands. On the basis of localization and morphology, the cells in 5-day-old primary monolayer cultures could be classified into 3 categories: (1) cells of the migration zone (periphery) of microexplants, (2) single cells, and (3) monolayer cell islands. These cell categories showed little or no G6PDH activity in cultures of benign origin. In the corresponding histological sections of benign tumors no G6PDH activity occurred in the stroma, whereas the G6PDH activity varied in the epithelial elements, being highest in dysplastic elements. Apparently, these elements remain within the microexplants or never appear in the final cultures. By contrast, in cultures of malignant origin some of the single cells and in particular the cell islands showed high G6PDH activity. In histological sections of the malignant tumors the stromal cells showed no activity, whereas the epithelial elements in solid, invasive portions showed high activity. Studies on the established human mammary cell lines MCF-7 (malignant) and HBL-100 (presumptive benign) revealed higher G6PDH activity in MCF-7 than in HBL-100. Human skin fibroblasts revealed no activity. Electron microscopy of isolated cell islands after enzyme incubation confirmed that these were epithelial, because of the presence of desmosomes. Our observations suggest that G6PDH activity is a possible marker of at least some malignant cells in primary monolayer culture.