  Normal life activities between cells rely crucially on the homeostasis of the
cellular microenvironment, but aging and cancer will upset this balance. In
this paper, we introduce the microenvironmental feedback mechanism to the
growth dynamics of multicellular organisms, which changes the cellular
competitive ability, and thereby regulates the growth of multicellular
organisms. We show that the presence of microenvironmental feedback can
effectively delay aging, but cancer cells may grow uncontrollably due to the
emergence of the tumor microenvironment (TME). We study the effect of the
fraction of cancer cells relative to that of senescent cells on the feedback
rate of the microenvironment on the lifespan of multicellular organisms, and
find that the average lifespan shortened is close to the data for non-Hodgkin
lymphoma in Canada from 1980 to 2015. We also investigate how the competitive
ability of cancer cells affects the lifespan of multicellular organisms, and
reveal that there is an optimal value of the competitive ability of cancer
cells allowing the organism to survive longest. Interestingly, the proposed
microenvironmental feedback mechanism can give rise to the phenomenon of
Parrondo's paradox: when the competitive ability of cancer cells switches
between a too high and a too low value, multicellular organisms are able to
live longer than in each case individually. Our results may provide helpful
clues targeted therapies aimed at TME.
