Kinetics of tumor growth in arthritic versus non-arthritic mice. (a) Mice injected with 4T1 cells; (b) mice injected with TUBO cells. Compared with the non-arthritic Balb/c mice, a significant increase in tumor burden was observed in SKG mice challenged with 4T1 (** P < 0.01) and TUBO (* P < 0.05) cells. Note: All tumor cells were injected in the mammary fat pad and sacrificed four-weeks post tumor challenge. n = 10 mice per group.