I am so sorry to hear this news.  We did Palladia, but only for a week before Otis passed.  Izzy's Mom has a lot of experience with it.   Perhaps reach out to her?  I thnk I had started a forum topic on Palladia too, but dont remember whether there were a lot of comments.

I have arrived! Although I've replied to Tina directly, I also wanted to add information here so that others can benefit (or not! - not sure how much help I am) from the info I can share about my experience using Palladia. I will also add that if your dog isn't on a steroid - like prednisone - yet, ask the vet. It's really helped Izzy's tumor but long term use will cause muscle wasting.

First, Diamondback Drugs is a compounding pharmacy that will make generic Palladia for your vet at a fraction of the cost. Ask your vet if this is an option for you should you need Palladia. It is still expensive, but less so. Izzy took 75 mg every other day initially, decreased to 75 mg every third day until discontinued at roughly 6 months in (lost efficacy). She is on it again (because we got desperate) at 80 mg every other day. 14 pills costs roughly $375 USD, but your dog's dose will likely be different and the cost varies, logically.

Second, this drug worked WONDERS for Izzy's inoperable Mast Cell Tumor on her foot ... for as long as it worked. Izzy's onco hadn't really seen it lose efficacy previously - when it worked, it worked! - but Izzy also displayed the very rare side effect of pigmentation loss ... her black nose became brown/pink ... so she is clearly very special. Also, she keeps on living, so that could have something to do with it. That said, when we first tried it, Dr. Arthur said should could (and would need to) stay on it forever and ever to control the tumor. We've tried other drugs as well because her foot went crazy, but that's a different story.

Third, Izzy is (old as dirt and) nearly two years post OSA diagnosis with NO evidence of lung mets (knock on wood). I don't know if that is dumb luck or if the Palladia helped keep things that way. I would say that, if you can afford it, try it ... because it certainly won't hurt anything. 

Fourth, I don't know much about lung mets, but is radiation an option?? I did palliative radiation for Izzy's MCT and, at first, thought it didn't work. Turns out my girl is always special and does what she wants when she wants and this applies to her tumor as well. About 6 weeks after completing the treatment, her tumor started shrinking like crazy! Maybe the same would be true for lung mets? She was totally unaffected by the radiation and, even though she is a million, tolerated the anesthesia required (daily) to undergo treatment like a champ. So much so that she was mildly annoyed at momma for not letting her go back to the vet school to see her friends on the sixth day. (She didn't get that treatment was over.)

Lastly, as Teresa and beautiful Miss Cow have taught us all, mets schmetz. Manni and all of our babies have lots more living to do!