Guideline 72 - Supporting Material: Cochran’s Model for Calculating the Likelihood of Survival at 3, 5 and 10 Years

Guideline 72 - Supporting Material

Cochran's Model for Calculating the Likelihood of Survival at 3, 5 and 10 Years¹

USING COCHRAN'S MODEL

Derive a "risk-score" for the patient using the checklist above.
The likelihood of survival at each time point can be calculated using a mathematical constant derived from the survival experience of the patients studied. The probability of survival is calculated by raising the mathematical constant to the total product of all the weighted risk factors in the above table. The relevant mathematical constants are:
For survival at 3 years 0.987
For survival at 5 years 0.975
For survival at 10 years 0.960

EXAMPLE

Calculating the likelihood of survival at 3, 5 and 10 years for a male aged 40 with a melanoma on his back that has a Breslow thickness of 5mm and a 4mm broad area of ulceration.
Using the checklist the "risk-score" is calculated by multiplying together the weighted factors (1.8 x 1.0 x 2.6 x 3.8 x 1.5 giving a total of 26.7).
For survival at 3 years the calculation is 0.987^26.7= 0.7051 = 71%
For survival at 5 years the calculation is 0.975^26.7 = 0.5086 = 51%
For survival at 10 years the calculation is 0.960^26.7 = 0.3362 = 34%

Cochran AJ, Elashoff D, Morton DL, Elashoff R. Individualized prognosis for melanoma patients. Hum Pathol 2000;31:327-31.