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The Tumor Ecosystem: Cancer as an Invasive Species

Ecologists have studied the population biology of invasive species for decades and have documented their impact on local environments as well as the global ecosystem as a whole. Invasive species start as a native population within a defined community and are then transported by some means to a new environment. In this new environment, the invader either then dies off or enters a period of time during which it establishes itself (lag period). It then begins to spread and have impact on the local environment, disrupting the ecosystem as a whole. This disruption has broad implications for the native species and the broader ecosystem. Biologic traits that result in a robust invasive species include rapid proliferative capacity, adaptation to environmental stress (phenotypic plasticity) and high tolerance to environmental heterogeneity.

population biology of invasive species and matastasis

 

The life cycle of invasive species is directly analogous to the study of cancer metastasis (see figure). Cancer must grow in a primary site, extravasate and survive in the circulation to then intravasate at a target organ (invasive species survival in transport). Cancer cells often lay dormant at their metastatic site for a long period of time (lag period) before proliferating (invasive spread). Proliferation in the new site has an impact on the target organ microenvironment (ecological impact) and eventually the human host (biosphere impact). Chen KW, Pienta KJ. Modeling invasion of metastasizing cancer cells to bone marrow utilizing ecological principles. Theor Biol Med Model 2011 Oct 3;8:36.

A large proportion of solid tumor metastases are bone metastases, known to usurp HSC homing pathways to establish footholds in the bone marrow. Recent evidence suggests that tumor cells target and parasitize the HSC niche during metastasis just as invasive species do in the environment. Successful metastatic cancer cells grow in a primary site, emigrate out from that site, survive during migration, immigrate into the new environment and then naturalize and overtake/co-opt and/or cooperate with the host species to form a new tumor ecosystem.

Prostate Cancer Metastasis process diagram

Pienta KJ, Loberg R. The “emigration, migration, and immigration” of prostate cancer. Clin Prostate Cancer 2005 Jun;4(1):24-30.

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