Why cancer at the primary site and in the lymph nodes contributes to the risk of cancer death

BACKGROUND: Cancer at both the primary site and in the lymph nodes is associated with lethality, although the mechanism by which lethality arises from each site has been poorly understood. For breast carcinoma, each positive lymph node contributes an approximately 6% risk of death, and each millimeter of primary tumor greatest dimension contributes approximately 1%; whereas, for melanoma, each positive lymph node contributes an approximately 23% risk, and each millimeter of tumor thickness contributes approximately 8%: This is described by a pair of linked equations, the Size+Nodes method. METHODS: A simple expression, the ProbabilityEstimation equation, which was derived from the authors' binary-biologic model of cancer metastasis, was used to calculate the probabilities of spread of cancer cells from data on tumor size, lymph node status, and death rate. RESULTS: In this report, the authors demonstrated, that when similar masses of cancer are compared, the chance of lethal spread of a cancer cell to the periphery is approximately the same whether the spread emerges from a lymph node or from the primary site. The greater the number of cells at the primary site (tumor size) or the greater the number of cells in the lymph nodes (number of positive lymph nodes), the greater is the aggregate chance that 1 or more cells has undergone a lethal event of spread, a process captured by the Size+Nodes equations. CONCLUSIONS: The lethal contributions of cancer at the primary site and lymph nodes can be explained by a simple mechanical process of the spread of cancer cells occurring with definable probabilities per cell. The presence of cancer in the lymph nodes does not indicate an intrinsic change in a malignancy but, rather, an increased mass of cancer from which spread can emerge. Cancer 2009;115:5084-94. (C) 2009 American Cancer Society.