cellulitis in dogs

Question
my dog calvin,who is a black lab and the sweetest dog you'll ever meet, became very lethargic, wasn't eating and the biggest problem, could not sit or lay due to a "mass" on his chest by his rib cage. we took him to the vet and he was hospitalized. they hydrated him, did an ultrasound, but every day this mass would get larger. he is in a lot of pain and is being treated with pain meds and antibiotics. they said it is cellulitis, but i don't understand why this mass continues to grow. what is cellulitis and i would appreciate your thoughts. i am the biggest animal lover and this is breaking my heart. thank you for any opinions or help.  

Answer
Hi Geri!  I would definitely suggest a different veterinarian taking a look at Calvin.  Cellulitis is a skin infection that causes soft, red, sore masses on the skin.  It is a streptococcal or staphylococcal bacteria that enters the skin through a cut, puncture, ulcer, or sore, producing enzymes that break down the skin cells. It also spreads and is most common in lower limbs on a dog.
Calvin sounds as though he has a serious mass on his chest.  This should not be growing like this.  This mass needs to be removed ASAP and sent out for biopsy.  Labs and Golden Retreivers seem susceptible to cancerous masses, so getting this mass off of Calvin and sent off to biopsy would be extremely beneficial, as if this is a cancerous mass, getting rid of it will eliminate the cancer cells spreading.  Cancerous tumors do grow very quickly, which is why I am extremely suspicious of Calvin's mass.  
I hope this helps and please give Calvin MILLIONS of labby kisses for me.  I am a HUGE fan of labs...I grew up with yellow labs, black labs and chocolate labs.  My whole family is crazy about them!  I know what you mean by Calvin being the sweetest dog.  Labs have the most excellent personality and are SOOOO easy to love!  I can completely understand your concern.  If you have the time, please keep me posted and let me know how that adorable boy is doing.
Looking forward to hearing from you,
Hilary