Figure 1.

Two models of cancer progression: The traditional model (left) posits that all cancers are destined to follow an orderly progression from the primary site to the lymph nodes, on to distant metastatic sites, ultimately causing cancer death. The contemporary model (right) is more complex and heterogeneous. Some cancers are metastatic at their onset (A), some never metastasize yet cause death from local invasion (B), while others follow the traditional model (C). Still other cancers are not destined to ever cause symptoms because they grow so slowly that patients die from other causes before symptoms appear (D), stop growing (E), or regress (F).