One of the most important predictors of recurrence and survival in colorectal cancer is the presence of metastasis. The spread of tumor cells dictates treatment decisions depending upon whether the metastasis is to local lymph nodes or to distant locations. Traditionally, a linear model of progression has been taught and used for staging and treatment where a uniform population of cells acquires the ability to move to a lymph node and then to another and then metastasize to distant sites. Recently, there have been multiple studies that question this teaching. Advances in sequencing tools have increased our understanding of cancer genetics and have confirmed that tumors are genetically heterogeneous both between tumors and within tumors, and this alters our understanding and models of metastasis and tumor evolution.
