I was diagnosed with stage 2 BC in April after 8 rounds of chemo I had a benign lump removed and some tissue as the lump had gone from the chemo - the margins in the breast came back clear!
The sentinel lymph node and a few others were removed as a precaution they always came back clear on the scan but the pathology report tested positive for cancer cells and now I have to go back to see the surgeon tomorrow who has booked another operation on Monday! She said she would explain all tomorrow but meanwhile I am sat here freaking out! I am sure it’s a case of removing what’s been left behind than anything else! I thought I was over all this now I feel like I have gone back to square one mentally! 
So sorry to hear that cancer was detected in the Lymph nodes on biopsy. That must have been a huge shock after the scans being clear and the clear margins.
I had cancer in my lymph glands detected from the start (as well as the lump) so spoke in length to two different consultants about my options.
As my breast lump was large we decided to do chemo first and then see what happened. The plan was to shrink the lump and see if we could get away with a lumpectomy. They wanted to do a node clearance anyway.
The lump shrank dramatically through chemo so a lumpectomy went ahead. The consultant however still wanted to do a level one node clearance as that was their standard proceedure.
I read up on this and decided for a SN biopsy instead. I was lucky in that this was clear. The consultant had warned me that it would be harder to do a lymph node clearance after a SN biopsy.
There is a trial being carried out in the UK called POSNOC. There is a question mark over treatment to the arm pit if cancer has spread to the lymph nodes
The options in general are
to operate again and remove more lymph nodes (sounds like what your consultant has planned)
to radiate (I am having that now)
to use chemo (we have both had that)
or just use hormone treatment / targeted treatment. (I am having Herceptin)
and probably other things I don’t know about.
This is something that your consultant should be discussing with you. We need to give unformed consent to any proceedure and I can’t see how you could do this without talking all the alternatives through with them first.