Serial transplantation, histology and cellular kinetics of a rat adenocarcinoma

Data are reported on the growth, histology and cell population kinetics of a spontaneous mammary tumour in the rat at the 1st and 35-40th transplantation generation. With serial transplantation subcutaneously in isologous animals, the macroscopic growth characteristics of the tumour did not alter. The tumour had a volume doubling time of approximately 1.6 days at 400 mm3, increasing to about 7 days at 20,000 mm3. The histology, however, changed dramatically from that of a well differentiated papillary adenocarcinoma with a well defined vascular pattern and minimal necrosis to become by the 35th generation a poorly differentiated pleomorphic cellular tumour in which stromal elements and associated vascular supply were minimal and necrosis prominent. These changes were not manifested in the median cycle time of its cells, 16-18 hr, but by an increase in the growth fraction from 0.36 to 0.59 with a commensurate increase in the cell loss factor from 0.04 and 0.30.