I asked a radiologist this and he didn’t know the answer, so up it goes on my blog. Perhaps someone can answer it? I have a few hypotheses that depend on the answer.

When microcalcifications tend to occur in association with
unilateral cancer (in breast cancer, for example), why do they tend to
occur bilaterally in the same region of tissue?

I’m wondering whether this might indicate an underlying genetic or environmental factor that affects both organs and predisposes to, but is not sufficient for, carcinogenesis (if it were sufficient on its own, I’d expect cancers associated with bilateral calcifications to be bilateral themselves). Another possibility is that the presence of cancer itself causes the calcifications, but the only
thing I can think of that would cause them bilaterally is some sort of regional immune/inflammatory response to the cancer.