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Host Resistance


A tumor does not grow freely in its human host as it would in tissue culture. The host puts up a defense, generically called “host resistance”, which resembles defense against infections. There is a homeostatic interaction between the host and tumor cells or microorganisms based on a dynamic balance between them and the host microenvironment in which they grow - an updated version of the seed-and-soil hypothesis. The tumor arises from an abnormality of growth and differentiation based on altered structure, regulation and expression of its genes. The resulting properties of transformation, invasiveness, metastasis, clonality and heterogeneity give rise to its malignant behavior. But the outcome of its growth still depends on its interactions with host defenses for a net result of progression, dormancy or regression. The process is dynamic and chronic with the balance of host resistance changing with the advancing stage of tumor growth.