Kalam

[Jehanne]

Then, let's get practical -- what do both of you think the cause(s) of malignant tumors are?

Using the term "cause" in the Aristotelian/Thomist way, the causes of a malignant tumor are all the things that must be the case for a malignant tumor to exist. 

These include the malignant cells, whatever mechanism made them become malignant, the living body on which the tumor lives, the laws of nature which govern the ways in which the chemical/biological actions take place, the time/space of the universe in which the laws of nature operate, etc. 

Since the tumor is something that appeared after the body of the patient, this is a case where there is a temporal element. (The passage of time is also one of the causes.) However there are also cases in which the temporal element is not a relevant part of the causal chain.

In a per se series, of the kind that Aristotle deals with, "prior" means it is higher up the chain of necessary things. So the laws of nature are prior in the sense that you can imagine a world with laws of nature but no tumor, but you can't imagine a world with a tumor but no laws of nature.

Aristotle wrote in Greek and Thomas in Latin. I agree that the English translation "cause" is misleading to modern people. "Necessary conditions" might be better.

I am okay with everything that you state, as long as it is understood that there are events that just happen (e.g., the radioactive decay of one atom versus the nondecay of another) that are not caused by anything; they just happen.