onco-

A tumour.

Greek onkos, mass.

Oncology is the study and treatment of tumours; something oncogenic causes development of a tumour; an oncogene is a gene which in certain circumstances can transform a cell into a tumour cell; oncolysis is the destruction of a tumour, usually in response to treatment; the adjective relating to tumours is oncotic, but it can also refer to an increase in volume or pressure. See also ‑oma.