Neoplasm (from Ancient Greek νέος- neo "new" and πλάσμα plasma "formation, creation") is an abnormal growth of tissue, and when also forming a mass is commonly referred to as a tumor or tumour.[1][2][3] This abnormal growth (neoplasia) usually but not always forms a mass.[4]
The World Health Organization (WHO) classifies neoplasms into four main groups: benign neoplasms, in situ neoplasms, malignant neoplasms, and neoplasms of uncertain or unknown behavior.[5] Malignant neoplasms are also simply known as cancers.
Prior to the abnormal growth of tissue, as neoplasia, cells often undergo an abnormal pattern of growth, such as metaplasia or dysplasia.[6] However, metaplasia or dysplasia do not always progress to neoplasia.[1]