core biopsy tomorrow worried

I was diagnosed initially with stage 4 bc in Sept 03. I've been on chemo ever since (taxol/herceptin then taxotere/carbo/herceptin).

Most of the mets have been cleared. Still one in the abdomen.

My last CT scan showed increased thickening in left breast (site of bc). It could be lymphodema -- I've had a lymph node disection - and a swollen breast ever since (June 04).

But it could be more cancer.

So my docs are doing a breast MRI and a core biopsy.

I'm wondering what to expect with a core biopsy. Is it very painful?

I'm also, of course, worried that it will show progression.

Thanks in advance. Elayne.