Raised lumps under my cats armpit

Hi what could this be under my cats armpit hes a done male who goes outside a lot upto date with flea and worming

I don't know what that is.  It would be a good idea to show it to your vet to have it checked.  Even if they don't know either, they may elect to trial treat or do a biopsy to find out more.   If it's itchy or being intensely licked, I might tend to wonder about allergies / stings etc. first. - the concern about these is that the area may expand with licking etc.  If it isn't itchy, I might think about skin tumours or autoimmune disease.   Either way, it doesn't look like something to ignore. If you do find a diagnosis, we'd be interested to know.