Influence of platelet lysate on colony formation of human breast cancer cells.

The effect of platelet lysate on the growth of human breast cancer cells was studied in the two-layer soft agar culture system. Lysate was prepared from frozen-thawed outdated human platelets. Eighteen to 446 colonies (mean: 85) grew from 50 of 57 tumors plated at a density of 5 X 10(5) cells/plate, yielding control plating efficiencies from 0.004-0.089. The viability of the cells plated ranged from 10-80%. All tumors were also plated with 200 micrograms/ml platelet lysate. Significant enhancement of colony formation (CF) (p less than 0.025) appeared in 26 of the 57 tumors tested. The number of colonies grown from these 26 tumors ranged from 36-580 (mean: 152). The extent of enhancement varied from 1.25-3.19. Significant suppression of CF (p less than 0.025) appeared in 6 of the 57 tumors. The extent of the suppression varied from 0.35-0.67. Platelet lysate induced no change in CF in the 7 tumors that failed to form colonies in control plates. There was no relationship between tumor cell viability and either the number of colonies appearing in control plates or the response of CF to platelet lysate. By contrast, there was a significant correlation (p less than 0.005) between viability and the extent of enhancement of CF by lysate. Concentrations of lysate varying from 50-400 micrograms/ml did not yield a consistent dose-related increase in CF. The results indicate that platelet lysate significantly enhances colony formation from a substantial percentage of human breast tumors.