Can non aggressive breast cancer metastasize to bone? I have er/pr+, her2- breast cancer w tumors in spine and rib. Dr unsure both are related.

Yes, unfortunately. Unfortunately, er/pr positive, her2 negative breast cancer metastasizes to bone quite commonly. On the good side, it usually responds to treatment with hormonal therapy, radiation, and bone strengthening medications very well and patients can live for years. If this is the first possible sign of metastatic disease it is often reasonable to get a biopsy to confirm the diagnosis.
Might be. Common things are common - meaning it is more common for one cancer to have spread than it is for there to be two cancers. Your doctor will perform some tests to get the answer. Hope this helps, and good luck.
Yes. Yes, any breast cancer can spread to bone. That said, there is a lot of evidence that breast cancers which spread to bone first are associated with better survival than cancers that spread to other areas. And, of course, these bone lesions may not be cancer at all. It is probably worth a biopsy. Here's to hoping that the new year brings you a negative biopsy.