Do cancers only arise from cancerous cells?

Cancers typically arise from normal cells that undergo genetic mutations, leading them to grow uncontrollably and evade the body's regulatory mechanisms. While cancerous cells can proliferate and form tumors, the initial transformation often begins in healthy cells due to factors such as environmental exposures, inherited genetic predispositions, or lifestyle choices. Thus, cancer originates from the alteration of normal cells rather than exclusively from pre-existing cancerous cells.