Obesity-associated circulating factors promote greater breast cancer cell viability and growth. (A) MCF-7 and T47D breast cancer cells were exposed to 2% obese (Ob) or control (Con) patient sera for 48 hours; viability was then measured by MTT assay. (B) Colony formation assay was utilized to assess MCF-7 and T47D cell growth following a nine day exposure to 2% Ob or Con patient sera. Data shown represent the average of at least three independent experiments. *, P < 0.05; **, P < 0.01 in comparison to Con. MTT reagent, 3-(4,5-dmethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide.