WHAT IS CANCER? Part II

9. How does cancer spread?

Most cancer cells that enter the bloodstream or lymphatics do not cause metastases. Only rare malignant cells actually survive to cause distant tumor implants by recruiting new blood vessels. Many cells do not seem to come to rest in tissues conducive to their growth. Perhaps others are extirpated by the immune system.

10. Does this process have an effect on how surgeons treat patients with cancer?

Operations to treat benign conditions are designed to remove as little tissue as possible while creating a new and desirable physiologic or anatomic state. Cancer operations, on the other hand, are designed to remove as much tissue as possible while leaving the patient with acceptable function. Cancer operations typically remove the primary tumor as well as the lymph nodes draining the primary site. Surgical resection is the single most effective treatment for solid tumors.

11. Why are lymph nodes removed during cancer operations?

More than 100 years ago, William S. Halsted (if you don't know the answer to any historical question posed on rounds, you should always guess "Halsted") appreciated that tumor recurrence on the chest wall after mastectomy was related to tumor in remaining lymph nodes. Halsted believed that cancer of the breast spread in an orderly fashion (or perhaps even contiguously) from the primary tumor to regional lymph nodes and eventually to distant sites. He popularized en bloc dissection of the breast with axillary lymph nodes for treatment of breast cancer. Conceptually, this approach was adopted for surgical treatment of most solid tumors.

12. What is a sentinel lymph node?

Sentinel lymph nodes are the first stop for tumor cells metastasizing through lymphatics from the primary tumor. Often there is more than one sentinel node, even for a small tumor. If no tumor is present in a sentinel lymph node, it is unlikely that tumor is present in any of the other nodes. Sentinel lymph node mapping has been used for cancers of many organs (including the skin, breast, colon, thyroid, and head and neck neoplasms). Careful evaluation of sentinel lymph nodes has proven reliable in the staging of melanoma. It will probably prove equally successful in managing breast cancer and head and neck tumors, sparing many patients far more morbid lymphadenectomies (lymph node dissections).

13. Do solid tumors spread in an orderly way?

Not necessarily. Another view of breast cancer behavior became popular by the 1970s. Bernard Fisher postulated that cancer is widespread at its inception. He stated that "breast cancer is a systemic disease … and that variations in effective local regional treatment are unlikely to effect survival substantially."

14. How do these different models of cancer affect treatment?

Surgeons who believe that tumors spread in an orderly way tend to perform complete lymph node dissections in concert with resection of the primary tumor. They generally believe that lymphadenectomy will cure some patients who have lymph node involvement without distant metastases and that local recurrence is a preventable cause of death. Surgeons who believe that lymph node metastases are simply markers for systemic disease are usually far less aggressive in performing lymph node dissections because (in their view) removal of lymph nodes that contain tumor will not cure patients who probably already have metastatic disease.