HDC and cancer: These effects were reverted by histamine administration.50 In this line, the histamine-producing probiotic hdc+ Lactobacillus reuteri decreased the number and size of colon tumours in HDC KO mice and reduced the gene expression of proinflammatory cancer-associated cytokines, indicating that histamine can suppress colorectal tumorigenesis and the severity of inflammation-associated colon cancer.38 On the other hand, endogenous histamine contributed to the tumour growth in a model of breast cancer developed in HDC knockout mice by suppressing the antitumour immunity.51