Notes

Sections

Extracellular Effects

To set up the diagram, we show the extracellular matrix and a blood vessel. Then, we draw a cancer cell, and show that it undergoes clonal expansion and diversification to form a primary tumor; this development was enabled by the physiological changes we indicated, above.

Cancer cells trigger angiogenesis

Formation of new blood vessels from existing vasculature enables the tumor to meet its nutritional needs.
— Interestingly, the "angiogenic switch" is triggered by tumors greater than 2 cm; below this threshold, simple diffusion suffices.

Cancer cells invade and metastasize

This enables them to cross anatomical boundaries. In contrast, the growth of benign tumors is limited by anatomical boundaries.
Steps:
- Cancer cells break free from the primary tumor.
- They invade the extracellular matrix and migrates to a nearby vessel.
- Then, in a process called intravasation, the cancer cells enter circulation. Be aware that cancer cells can enter blood and/or lymphatic vessels, and that some cancers are more prone to a specific vessel type.
- Cancer cells travel within the circulation, where they can form an embolus with T lymphocytes and platelets. This aggregation may protect the cancer cells from destruction.
- Cancer cells can break free from the embolus and exit the vessel, a process called extravasation.
- In their new environment, the cancer cells can proliferate to form a metastatic tumor; show that this tumor can also develop its own blood supply.
Be aware that invasion and metastasis are major causes of morbidity and death from cancer.

Cancer cells evade the immune system

Ensures their own survival.
— They can downregulate expression of MHC proteins and presentation of antigens on their own cell surfaces. Thus, they "hide" from the immune system.
— They can also suppress immune cell responses and release immunosuppressive cytokines, which dampens the ability of the immune system to defend the host.