The Hallmarks of Cancer: 8 - Tumor-Promoting Inflammation
After a too-long hiatus, here is my eighth article in this series :) The Hallmarks of Cancer are ten anti-cancer defense mechanisms that are hardwired into our cells, that must be breached by a cell on the path towards cancer. The Eighth Hallmark of Cancer is defined as “Tumor-Promoting Inflammation”. All seven previous Hallmark articles can be found here: http://goo.gl/IDGfLp
As always, because this is such a complex topic, I don’t want to skip details at the cost of avoiding TL;DR. So I’ve written a far more detailed explanation (complete with my own diagrams!) that is easier to follow on +Scientific American, and I highly recommend you check it out here: http://goo.gl/ThMpl9. In this article, I explain the complex relationship between inflammation and cancer, and how our own immune system can ‘turn traitor’ and promote cancer development.
✤ Within the last few years, we have obtained clear evidence that inflammation plays a critical role in cancer development, and we are just beginning to understand the molecular mechanisms of how this happens. Chronic infections, obesity, smoking, alcohol consumption, environmental pollutants and high fat diets are now recognized as major risk factors for most common types of cancer; and, importantly, all these risk factors are linked to cancer through inflammation.
✤ Inflammation is how tissues and cells respond to injury. If the inflammation causing agent persists for a prolonged period of time, the body’s response to it becomes a chronic inflammation. Chronic inflammation increases cancer risk.
✤ An extremely graphic yet apt way of describing a tumor is as “a wound that doesn’t heal”. Indeed, there are many similarities between a cancerous tumor and the process of wound healing. Both involve the growth, survival, and migration of cells; both require the growth of new blood vessels; importantly, all these processes are controlled by growth factors and signalling molecules. Just as the immune cells gather near a site of injury to secrete growth factors to begin tissue repair, tumors can also surround themselves with immune cells that secrete these same growth factors to promote their uncontrolled cell growth.
✤ Tumor Associated Macrophages (TAMs), a ‘corrupted’ type of immune cell support tumors in four different ways; by providing growth factors, helping to develop a blood supply to the tumor, promoting metastasis and suppressing the tumor-killing abilities of the immune system. Essentially, TAMs help the tumor overcome the barriers represented by the anti-cancer defence mechanisms that consist the Hallmarks.
✤ The existence of both tumor-promoting and tumor-killing immune cells at first seems counter-intuitive. The immune cells specializing in wound cleaning and clearing up dead cells are recruited and subverted by tumor cells to support tumor growth and progression. Shifting the balance from tumor-promoting to tumor-killing immune involvement therefore represents an attractive and powerful possibility for future therapy.
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