I have gone through your query. Lump you have mentioned here might be the thickening of the skin due to running. This thickening is harmless(at present) and is due to stress
on that area during running.
There are chances that it will convert to CORN
, which will be very painful and will require excision.
I advise you to wear good quality of socks and shoes for running.
Do consider a positive feedback as a credit to my work. Let me know if you have any further questions.