Reading the prognosis of the individual with breast cancer

Abstract The well-established Nottingham Prognostic Index (NPI) places patients with primary breast cancer into Prognostic Groups with significantly differing survivals. However, mean survival of two adjacent groups may differ by a maximum of 22%, so that patients with NPI’s with only a 0.1 difference but lying in different prognostic groups may apparently have large differences in prognosis, whereas two patients lying in the same NPI group but with NPI’s differing by 0.9 are given the same prognoses. Aim To obtain better survival estimates for the individual than is provided by placement in an NPI group. Method Consecutive primary operable breast cancers treated at Nottingham City Hospital 1990–1999. Ten year % actuarial survivals plotted for 10 ranges of NPI from 2.0 to 6.9. There is an excellent inverse correlation between median NPI value for each range and survival at 10 years. To enable estimation of survival for all individual values of NPI, a curve fitting technique applied to these results (by G.B.) gave the formula to estimate survival from the individual’s NPI score: 10 year % survival for the individual = −3.0079 × NPI 2  + 12.30 × NPI + 83.84. This gave an r 2 of 0.98. Results and conclusion Greater accuracy in individual survival prediction is obtained by dividing women into 10 groups by NPI scores than in the originally described six groups; rank order of survival in relation to NPI score is preserved. A curve fitting technique has been applied to these data to give a formula for the prediction of 10 year survival for every 0.1 value of NPI.