HDC and mastocytoma: Cellular histamine content was drastically increased in the presence of dexamethasone (>8 fold at day-16, Figure 3a), which is consistent with a previous study that exhibited the dexamethasone-mediated induction of histidine decarboxylase (HDC), which is the rate-limiting enzyme for histamine synthesis, in a mouse mastocytoma, P-815 [18].