Hi and welcome to HCM,thank you for your query.
Usually pus indicate subcutaneous infection due to follcilitis,abscess
or some other. cancer is rare at this site with such manifestation especially in your age so this is the last thing to think of. You should just visit doctor who can evaluate is it necessary to prescribe antibiotics or it must be surgically drained. Also,biopsy
can done to be 100
% sure about diagnosis. but i am sure that this is just lipoma
or inflammated ateroma.
Wish you good health. Regards