Table 2. The values of the probabilities of various events of cancer spread.

Metastatic event	Probability of spread per cell p=-ln(1-L)/N	Source of information for the value of L	Value of p the probability of spread per cell for tumour masses of ∼5 mm	Nature of relationship between the value of p and tumour size
Lethal spread of breast cancer from the primary site in the breast to periphery, pathway unknown	p BC-overall	LBC-overall=the fraction of breast cancer deaths among all patients	8.27 × 10−9	p=aNb aBC-overall≈0.000056 bBC-overall≈-0.56203
Lethal spread of melanoma from the primary site in the skin to periphery, pathway unknown	p MEL-overall	LMEL-overall=the fraction of melanoma deaths among all patients	1.23 × 10−7	p=aNb aMEL-overall≈0.027 bMEL-overall≈-0.7836
Nonlethal spread of breast cancer from the primary site in the breast to the lymph nodes	p BC-to-nodes	LBC-to-nodes=the fraction of node positive patients among all patients	1.75 × 10−8	p=aNb aBC-to-nodes≈0.000092 bBC-to-nodes≈-0.69251
Lethal spread of breast cancer from the lymph nodes to the periphery	p BC-from-nodes	LBC-from-nodes=6.08%, the lethal contribution per positive lymph node	7.96 × 10−9a	Undefined

^aThe size of nodal metastases was found to have a mean value of 5.3 mm (Table 3). The value shown here for p_BC-overall is for a mass of 5 mm; for 5.3 mm, p_BC-overall=7.49 × 10⁻⁰⁹.