What Causes Development Of Lump On Shin Bone?

My son is 27 yrs old and has played football for yrs semi pro He has developed a lump on his shin bone.That has gotten larger n he has some pain My husband and I git him to go to Drs they ordered an X-ray which was done n it came back inconclusive Now Dr wants blood work wants to see results then an,MRI Why blood work are they looking for bone cancer? He has had this lump for quite sometime before we convinced him to get it checked out! Can I have your thoughts please I m very worried