Almost any tumor can be removed, but in some cases, the rat's quality of life may not be worth it. If a rat is very old or is very sick, the operation may be more life-threatening than the tumor itself. An abscess springs up around a wound, though you mat not have seen the wound. If it suddenly sprang up in a matter of hours and grew very quickly, it is probably an abscess, especially if it is hard. A malignant tumor is also hard, and it grows quickly, but not as quickly as an abscess.
Malignant tumors are usually more oddly-shaped and more firmly attached.
My rat is bleeding vaginally. Rats do not have menstrual periods. Yes, you can spay and neuter rats. In females, spaying prevents tumors and makes her live longer. Neutering in males may stop the risk of prostate cancer.