9 yr old Chihuahua has 3 masses on breast

Question
My senior Chihuahua got spayed today and had a mass taken out. When I got home I noticed she had two more small masses next to two of her niples.They are round, hard and under her skin. The mass that that was taken out today was round, small and had a brownish color. Can this mean she has cancer? Is there any medication I can give her to treat this condition without going through surgery again?

Answer
I don't understand why the vet didn't remove those lumps either.
Yes she has mammary cancer which results most of the time from not being spayed at a young age. This is why we try to emphasis spaying under the age of one year.

Mammary tumors, once they start showing up, seem to just come back over and over. Which means more surgeries to remove them. They will not stop on their own and there is no medication to stop or remove them.
You will have to just keep getting them removed. Chihuahua's seem to really be prone to getting these when they are not spayed but all dogs can get them. Most of the breeds we saw with them are smaller dogs.

Don't wait until these tumors are large as there isn't much skin to replace them with the larger they get. Removing them when small is the safest and smartest way to go.