Advice-how to approach another Surgery after many b4 it went wrong

Hello, My dog (10yr pit bull) has had to have many surgeries, some related to mammary cancer, some related to other lumps (some were cancerous - some werent). Almost all her her surgeries have gone "bad" on the healing side. We have gone months "open healing" on more than one occasion. In one case she had to have a small lump from her toe removed and half her toe ended up becoming infectious goo, and she had to grow the whole thing back. FYI: She has an immune system issue that requires a constant daily regimen of CycloSporine and Ketoconazole (or her feet/lets get infected and chews them badly. All other meds and options have been tried prior - including one vet having her on steriods - which worked on but my new vet did not like that approach). This brings us to today. She has a new cancerous lump on her knee, and a mammary that me and the vet have been "ignoring" because of the issues on other surgeries. The knee cancer lump is not related to the mammary. I even had them xray her to look for nodules to make sure she looked clean inside to have all the info I thought I would need - and it came back good and clear. They also could not manually feel/find anything in the lymph nodes. They are now advising we need to remove the mammary as it keeps growing - but they are even more concerned about the knee as they think it will affect/take away her mobility if allowed to continue to grow. I want to do what is best, I want my dog to live as long as possible, but her quality of life has been rough the last couple of years due to constant surgery and 3-6 month heal times (open wound healing normally). She is finally happy again lately. I have not seen it in a while and breaks my heart to think of her becoming depressed again. The vet has me convinced I need to do this, I am pretty sure I need to do the surgery. Is there anything I/the vet can do to make sure this one has better results on healing/no infection/immune system attack? I thought I tried everything in prior times and followed all vet advice. I have attached pictures of the results of a mammary removal (her put under twice and mammary sewed up twice - including the original surgery - before we gave up and went open healing. ) Any advice/thoughts would be highly appreciated! Thanks, Mike Warning: Graphic images (it is only allowing 3 so I will show the bad pictures instead of including how it looked freshly sown before it went "bad")

Hello and Im sorry that you find yourself in this situation.  I think you may perceive this as a 'damned if you do, damned if you don't' situation; the lump is potentially serious but you are not removing it because the alternative, removal, might end up being serious - so you are not sure what to do.   I am not sure either; it sounds to me as though your vet ought to 'stage' this lump; to figure out what it is and, if its cancer, what stage of cancer and how far it has spread.  They may approach their pathology laboratory team to work out what action is most desirable.  In my experience with complex lumps, speaking to the pathology lab before removing a lump can be helpful.  If its a mast cell tumour or lymphoma for example, there may be chemotherapy options.  If it is inflammatory, then cutting tissue away may not help.  Finally, a lab may be able to guess how the lesion is likely to behave in advance, based on statistics from other cases.   Encouraging your vet to consult their pathology lab prior to acting, could change what they do.