PTGS2 and neoplasm: In comparison to the non-arthritic Balb/c mice with tumor challenge, the expression of COX-2 in the bones of the arthritic mice was significantly greater even without any tumor (Figures 5a, c, e, and 5f), which was undeniably augmented when these arthritic mice were challenged with the 4T1 tumors (Figures 5b and 5d) but not with TUBO (data not shown).