This is Dr. David
if you have had surgery in the area before, that small lump could very well be scar tissue from the surgery or a small benign lymph node in the left groin.
prostate cancer would not spread to the groin lymph nodes.
but just by feeling, you can't tell for sure. an inguinal ultrasound is a good test to get more information about the lump
and see if it is scar tissue or a benign lymph node or a benign cyst.