Figure 4. Epigenetic context in tumourigenesis.

1. Tumours can develop from progenitors that provide an epigenetic context for the establishment of epigenetic patterns, which can be identified by an active gene silencing pathway. Aggressive T-cell lymphomas provide an example, as they maintain properties of their T-cell progenitor origin such as SATB1 expression.
2. Other tumours are thought to establish a similar cellular context when they progress to malignant disease. Breast cancer cells provide an example for this type of tumour. When breast cancers progress to a more malignant and highly metastatic phenotype, SATB1 expression can be elevated. This might go along with a reprogramming of the tumour cell transcriptome, and albeit direct evidence is still awaited, with the re-establishment of pathways for gene silencing. In breast cancer SATB1 expression is unrelated to the cellular context from which the tumour originated and is acquired at a late stage in tumourigenesis. Establishing a progenitor-like context might endow tumour cells with developmental pathways that contribute to metastasis.