9 year old Lab/Spaniel mix 'benign fatty tumor' now has issues?

2 yrs ago posted about this dog with small fatty cyst on hip squishy and loose and caused no pain. Diagnosed as Lipoma (fatty tumor) Benign. Now, 2 yrs later in one week mass has grown to 5-6X size, dog exhibiting discomfort when mass is grabbed, hot to the touch. BEFORE I take her to the vet- and you all will scream that I do so, I know the drill, I want to know about the possibility of this being an abscess. Normally any unknown mass that grows that fast would be CANCER! to me, I've lost 3 pets to cancer. But the heat on the mass, + the proximity to a lot of hair (on the hip) and the anal glands, etc. I am first thinking abscess. I plan on shaving the area tomorrow and looking for a wound or outside cause, also expressing the anal glands although this dog has never had an issue...Anyway, would like to know if anyone knows through experience if a 'harmless' cyst can suddenly abscess and the best treatment for it- because if the cause is internal- ie: I can't open, drain, treat and medicate the abscess myself, then I need a vet

Thanks in advance