She developed a fairly significant lump sometime between the beginning of December and mid January. It's about 4 cm long by 2.4 wide.
Vet did bloods first and said they came back with no indication of anything sinister, although she is apparently mildly anaemic. She then had a fine needle biopsy done last week and we've just got the results.
"Insufficient sample, no clear indication of malignancy, but spindle cells present." 
Vet says she wants to just go straight ahead and remove it, but my poor old girl is almost deaf, doesn't have good sight and has developed late onset separation anxiety as a result. She has never coped well with inpatient procedures at the vets anyway and I'm really worried about how she would handle an op.
Complicating things are my own hang-ups arising from a monumental mishandling of my beloved boy's cancer years ago. They fluffed the biopsy - came back 'contaminated cells' so no clear cancer type identified. I had asked them to aspirate the regional lymph-node and they contaminated that as well. They insisted it was 'mast cell' - I was conversing with a vet online that said it sounded scarily like fibrosarcoma to him and that if it was, they shouldn't excise but amputate, as excision was likely to lead to accelerated growth (they couldn't get wide enough clean margins, as it was located on his hock).
Vet (actually a retired vet locum drafted in to cover small animal practice during the foot and mouth crisis) insisted I was making a fuss about nothing, removed the tumour and within months it was back, twice the size and growing rapidly, ultimately rupturing. In the meantime our dog went went from a nearly 9 stone hulk of gorgeous boy to skin and bone in just a couple of weeks. 
At that point the head vet of the practice got involved and finally admitted that the original vet should have listened to me in the first place. They wanted to get him straight in to amputate - sedated him for xrays to check for metastases, but it was too late. Every organ in his body had been invaded and we had to take the decision not to wake him. We lost him when my first dc was just 10 days old. It was fibrosarcoma, they had failed to remove it all and caused the rapid development in growth, end result, we lost him much sooner than we should have.
So, as you can imagine, I was more than a little 
to find yet another biopsy cock-up ten years later and several hundred miles away from the previous vets.
I have just tried to google, but don't have enough info to go on. From what I've read though, there is a chance, albeit small, that this tumour could also be fibrosarcoma and although they could get wider margins, I don't want to put my girl through the same torture that my lovely boy went through all those years ago, only to lose her in a few months anyway. I would rather keep her comfy and happy for as long as we can, iyswim.
Am I letting my heart rule my head here? I can't seem to make logical sense of it all and I desperately want to do the right thing by her.
Any thoughts, advice would be really appreciated.