A blastoma is a type of cancer that is caused by malignancies in precursor cells, often called blasts. Examples are nephroblastoma, medulloblastoma and retinoblastoma The suffix blastoma is used to imply a tumor of primitive, incompletely differentiated (or precursor) cells, i.e., chondroblastoma is composed of cells resembling the precursor of chondrocytes.

Blastomas usually occur in children.