Hi dr, i fell down on my slippery floor last week, a few days later i realize i have lump few cm under my elbow, doesn't hurt. is it cancerous?

Unlikely: If you fell on the same elbow , you could have injured the bursa (a small sac of fluid ). This can result in traumatic bursitis, and will require a little time to heal. A hard lump is not uncommon as it heals and should resolve in a few weeks. If it persists, becomes red, painful or enlarges then you should seek medical care .