rat oncology/illness

Question
Hi and thank you!  We have 4 beautiful rats, one of whom has lost significant weight in the last 2 months.  in the last few days she has developed what would appear to me to be a cervical lymphadenopathy (Im a human doc but certainly not a vet) and looked ill. She has about a 1/2 cm firm mobile lump under her left jaw bone that extends a bit caudally.  She also has an unusual chemical-like (hard to describe but somewhat unpleasant)odor that is new within the last few days.  Her respirations appear a bit more shallow and rapid than usual but it is difficult to assess given that she has lost quite a bit of weight.  Behaviorlaly she has been sleeping on top of us which is characteristic of when she feels ill.  She has been sleeping more but she dideat voraciously when we came home today. Upon firther inspection of her lump it appears that one of the other rats may have bitten her superficially over the lump.  We are forlorn that she appears ill and it seems to me that if she has cancer it would be a lymphoma like process going on but given that she is eating and dows not appear in any respiratory distress or pain we have not made the decision to bring her in to be euthanized.  If she does have cancer are there treatments for this?  If the lump is infectious and related to the bite we would be reassured but at the same time she is a 2 1/2 yr old beautiful dumo rat with a white belly and I think she also likely has a comorbid oncological process going on.  Well be taking her to the vet in short order but curious if you have any thoughts or advice or know what the smell change may be related to.
Thanks for anything you have to offer.  Rats are such wonderful, affectionate pets and we would love to know more about this as we plan having rats in our home for a long time.

Answer
The question is - did the chin lump come before or after the bite? Abcesses can form really quickly on rats and can often feel like a little fatty tissue tumor or even rock hard (which makes them hard to distinguish from all the bazillions of tumors ratties are prone to). As far as the smell; without sniffing it myself I can't really give you any idea, but sick rats OFTEN have that distinct sickly sweet smell.. not entirely unpleasant but not really fun to cuddle with either. Its a very difficult to describe smell, but I've come to recognize it as "that smell of infection". If the lump under her chin is an abcess, as you know, they can be taken care of in short order and that may be where the odor is coming from. If it isn't an abcess, it may be a tumor, and it would be a good guess that she probably has cancer elsewhere in her body.. which would explain the weight loss.

Any kind of swelling/lump/tumor/'whatever' around the chin and jaw makes me very goosey, and its good that you're getting her to the vet.

Good luck with her! I hope she is on the mend soon! (Please feel free to write and update me after she has been to the vet.. I'd like to hear what is going on with her!)