She's a red tail boa about 5 feet long about 4 years old. I took her out today and noticed a lump about 1 cm behind her vent. This lump is smaller than a marble. There is a slight pink tone to the ventral scales where the lump is located. The lump is somewhat firm (dont want to squeeze too much). She doesnt seem to be in pain.

any likely diagnosees?

I dont know if this is an urgent matter so i would really appreciate your comments

Thanks