1. Pathways of Metastasis

2. Lymphatic System
Very extensive drainage system that returns water and proteins from various tissues back to the bloodstream

3. Lymph System ©http://www. medem

4. Lymphatic vessels are even flimsier than capillaries
Cancer just has to “push” the door in—does not require dissolving enzymes

5. Blood vessels
Cancer cells have access to the bloodstream just as healthy cells do allowing them to enter the bodies' general bloodstream
Once in the bloodstream, the cancer cells now have access to every portion of the body

6. Circulatory System ©http://library. thinkquest

7. Bloodstream is not as effective as the lymph system as it is flowing with greater pressure

8. Spreading of the cancer cells through surgery (uncommon)

9. Fertile soil theory of metastasis
In 1889, Stephen Paget proposed that cancer cells shed from an initial tumor were dispersed randomly throughout the body by the circulatory system

10. He called these circulating cancer cells "seeds" and proposed that only some seeds fall onto fertile soil--organs where they can grow
they encounter and then grow in the surrounding organ

11. About 30 years later, a researcher named James Ewing countered Paget's theory by arguing that cancer cells don't spread randomly throughout circulation in search of fertile soil

12. He suggested that cancer cells become trapped in the first small blood vessels they encounter and then grow in the surrounding organ

13. Physicians today still use the term “seeding” to explain which organs the cancer cells have spread