Most people on this site would be aware that it is wrong to try and use carcinosin to deal with tumors.

One thing that can cause tumors [ in human and other life forms ] is stress.
Is this a happy rat? . A happy rat will not have cancer [probably] .

If it is you need to locate the correct constitutional remedy for the individual under consideration . Then select a potency of that particular remedy and administer.

Is it a hot/cold rat. Is it thrsty , what foods does it like , what is the condition of its coat .etc-etc-etc.