I noticed today that my foster dog Zoe has developed this weird lump to the side of her abdomen. We went to the vet last Thursday for vaccines and it wasn't there then. My husband says he first noticed it yesterday. It's oval shaped and squishy. Does anybody have any thoughts or had something like this come up? Otherwise she is acting fine. We are going to call the vet in the am but I thought I'd see if anyone had any ideas about what might be going on! I attached some pics of it.

Is it on a mammary gland? Is it attached to the body, or just a lump in the skin?
Best to get it checked…could be something to worry about.

Is it a solid attached lump or moveable?

I would get checked out. It could be lots of things but the fact that it has gotten quite large in a relatively short amount of time would make it something to have the vet take a look at. I always have lumps and bumps checked and even ones that feel the same have come back very different when fine needle aspiration was done.

My old girl (almost 16) has had such a lump for quite a long time. My vet won't take a chance of an operation and so far, although the lumps have got very fibrous -they don't distress her. I totally trusted his opinion and it seems to have paid off - yes they are unsightly but we (Jewel and me) don't mind. The risk of an operation is greater and I do know of some bitches operated on to remove the lumps have had a much shorter life.
However the lumps did become infected earlier this year and this nearly claimed her but with constant homeopathic treatment the infection finally went.
I do give her a carcinosis nosode but I know that some don't have faith in homeopathic treatment. I don't think that there is a traditional equivalent though I stand to be corrected.

Thanks for all the input. I'm calling as soon as the vet opens at 8:30 today. The lump doesn't feel like it is attached to the skin. It is more to the side than one of her mammary glands. The timing really concerned me to since it seems to have come up in a day or two. My older dog has fatty tumors and another one of my fosters has cysts and this lump doesn't really feel like any one of those two things. I'll let you know what the vet says. Thanks!