If a lump grows fast anywhere on the body could it be cancer?

Yes, but there are other benign skin findings that grow rapidly as well. Many of those benign conditions are far more common than skin cancer, especially in young people. You cannot jump to any conclusion without a full medical evaluation.

Cancers don't grow that fast on body A traumatic injury with swelling and fluid, an allergic reaction, a hernia, an infected bite, all could cause a growth. If any occurs on your body go for a exam and possible biopsy.