EXOSOMES, EVOLUTION - and CANCER

Linda and a pitiful chestnut tree

How does this stuff come about?

Some new research from the University of Pennsylvania involves exosomes and their role in cancer.  Exosomes are, essentially, garbage bags tossed out of cells into the blood stream.  Or so they are usually characterized.  However, it appears that exosomes expelled from cancer cells (this research concerns melanoma) also are bristling with proteins called PD-L1, which bind to a receptor called PD-1 found on the surface of cytotoxic (cell-killing) T cells of the immune system.  This binding effectively neutralizes the T cell, thus facilitating the health and well-being of the tumor!  What a stupid situation! 

This work is only in its baby-to-toddler stage, but it promises to be a useful technique when it grows up.  But I am mystified:

How in the dickens does something like this arise?  My rudimentary understanding of evolution tells me that new traits in animals and plants arise spontaneously, and randomly, and that those modifications that survive and prosper are those that make a positive contribution to the entities’ prospects for reproduction.  But cancer cells make a profoundly negative impact on survival.  Also, the cancer itself does not reproduce in any sense of the term that I comprehend, hence any tricks that a particular cancer cell might develop to protect itself cannot be transmitted to cancer cells in another creature.  Yet here you have it: cancer cells tossing garbage sacks into the bloodstream, but sacks studded with little IEDs capable of deactivating any immune cells they might encounter that could do damage to the tumor.

Maybe there is a devil, after all.

https://www.cancer.gov/news-events/cancer-currents-blog/2018/exosomes-tumors-evade-immune-system?cid=eb_govdel