Hi Susie,
There are a lot of options here. For example, the axilla is commonly affected by Damp Heat lesions. These typically act 'with a vengeance' and have an inflammatory nature.
Xian Fang Huo Ming Yin is good for lesions close to/on the mammary chain.
Do you have any further information on this cat -tongue, pulse, active points, previous health history, gross appearance of the tumor (including what was seen intra-operatively)?
This kind of information can help a lot, as this is an unusual kind of tumor that is therefore hard to make generalizations about.
S