Oscar,
these are some really good and highly technical questions and I am sure that Brian will join in on this thread, since he is far more knowledgeable than me.

Since I am neither a doctor or clinical researcher I can only give it my best guess, from second hand information that I have gleaned. Possibly, another way of presenting ECS would be a cancer that is "poorly differentiated" or highly invasive, in other words a cancer not "differentiating" (from the root word "different") between tissue types (muscle, lymph, brain, etc.) and even bone.

I believe most treatment plans take this possibility into consideration , especially in advanced stage cancer patients. That is why most of us have multimodality treatment protocols.

Add to your list, the length of time that the tumor has been lurking. Genetic predisposition (this is not to suggest that if someone else in your family had OC that you are more at risk but rather the immune system in general) will also play a role as well as environmental factors.