Definition

A term that describes the differences between tumors of the same type in different patients, the differences between cancer cells within a single tumor, or the differences between a primary (original) tumor and a secondary tumor. These differences may involve the tumor’s genes and proteins. For example, some cancer cells in a tumor may have genetic mutations (changes) that aren’t present in other cancer cells in that tumor. Tumor heterogeneity can play an important role in how cancer is diagnosed and treated and how it responds to treatment.