Mast cell inhibitor cromolyn increases blood clotting and hypoxia in murine breast cancer.

Human breast cancer is extensively infiltrated by mast cells that contain powerful anticoagulants such as heparin, tryptase and chymase. To determine if human breast cancer is associated with mast cell activation, we measured the levels of mast cell tryptase (an indicator of mast cell activation) in the blood of 20 women with varying stages of breast cancer. The mean level of tryptase in women with breast cancer (10.3 +/- 4.2 microg/L) was significantly higher than in 50 normal healthy women without breast cancer (3.0 +/- 2.5 microg/L, p < 0.05 by two-tailed t-test). To explore the role of mast cells in breast cancer in more detail, we then carried out experiments that were aimed at determining if an inhibitor of mast cell function, sodium cromolyn, could increase blood clotting and hypoxia within subcutaneous implants of the 4T1 mammary adenocarcinoma cell line in mice. We treated tumor-bearing mice with 5 consecutive daily doses of sodium cromolyn (10 mg/kg, i.p.). An average of 30% of the periphery of the tumors from the 5 drug-treated mice contained large lakes of clotted blood that were not evident in any of the tumors from the control (untreated) mice. By computerized image analysis of tumors immunostained for a hypoxia marker (pimonidazole), the tumors from the treated mice had significantly more hypoxia (35 +/-12 % hypoxic regions, n = 5) than the tumors from untreated (control) mice (16 +/- 7%, n = 5). We conclude that sodium cromolyn enhanced peri-tumoral blood clotting and intratumoral hypoxia. These results suggest that mast cells may play an important role in regulating blood clotting and hypoxia within breast cancer. Copyright 2003 Wiley-Liss, Inc.