Bump on my female kitty.

This is my 9 year old female DSH. She has had this bump for about a month now and it is worsening. It is starting to smell and create this discharge. It doesn’t seem to bother her at all and she’s not messing with it. Eating, drinking, and acting like her normal self. What does this appear to be? Thank you!

Hello - this lump appears to be badly eroded from one side, and may involve the whole thickness of the skin.  While your cat is not acting as though they are in pain, it is difficult to imagine that this would not feel sore.  Unfortunately, cats are masters at hiding pain from their owners, which might explain the lack of interest that you are observing; the behavioural signs of pain in cats tend to centre around grooming and other signs of stress, often performed in secret.  I am not clear as to where-abouts on the cat this is, but I am concerned that it could be cancerous (skin, lymphatic or or mammary cancer for example).  Immune reactions eg to a foreign body or severe mastitis could also present like this, as could a purulent wound. Therefore it sounds to be important to show the area to a vet as soon as possible; they may have two equal priorities.  One is to ensure that your cat remains as comfortable and stable as possible; the other is to identify what is causing the lesion.  If this is not known from the outside, diagnosis may necessitate looking at the cells microscopically.  Depending upon your vets' suspicions in context, this could involve sampling or removal for biopsy.