Oh my god, the last picture takes me back to February of this year. The moment we had to put our Lana to sleep because of a similar tumor. Lana had metastasized breast cancer. No longer operable and we postponed it as long as possible, until the moment we noticed that Lana was in pain. Then we had no choice but to make the heartbreaking decision to let her go.
Hopefully, the outcome for this dog is different, but when I see the last picture, I fear that the future for her will not last that long. I hope I am wrong.
Getting to it before it is inoperable is definitely very important, as you know. I am sorry to hear that this happened to you and of course, to Lana.