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BMJ No 7119 Volume 315 Letters Saturday 22 November 1997
New method for expressing survival in cancerUse of percentage of 'normal remaining life' may be confusingEditorJayant S Vaidya and Indraneel Mittra propose a new way of presenting survival data in patients with cancer, which may also be applicable to other diseases.(1) However, several issues need to be considered before this new method is adopted for widespread use. A common misconception that patients have about life expectancy (for example, 75 years at birth for male infants in Britain) is that they would not be expected to survive beyond the stated number of years. Some may even rationalise to themselves that once they reach the age of 75 their 'time is up.' Clarification of every new term or concept introduced to the patient is necessary to avoid misunderstanding and subsequent distress. When one states that the life expectancy is, for instance, 15 years at the age of 60, this figure represents the median survival for that population cohort. In other words, if the survival curve is plotted for this cohort as a 'real life expectancy curve' (as, for example, in figure 2 in the authors' paper), the percentage survival at 'full' term of the 'normal remaining life' would be 50%. Thus, in the authors' figure 2, the 68% survival to full 'normal remaining life' in their cohort of patients with breast cancer who were node negative suggests not only cure but also a better survival rate than that of the general Indian population. Does this imply that the actuarial data from the Life Insurance Corporation of India was unrepresentative or, alternatively, that the disease process itself, perhaps in combination with the care received, confers a better prognosis than that of the general population? Another important issue is the interpretation of treatment effects. Suppose a particular treatment can prolong survival by an average of seven years and the study was conducted in a cohort of patients with a mean age of 80. This would be depicted in the real life expectancy curves as representing a total cure (that is, the cohort randomised to the treatment arm has the same survival curve as that of a general unselected population in Britain). When a 40 year old patient receives the same treatment, however, do we advise the patient that he or she would derive a survival benefit of seven extra years on average or a total cure such that the full normal remaining life, equivalent to 36 years in Britain, would be attained?
L B Tan BHF/Mautner senior lecturer in cardiovascular studies
Regional Cardiothoracic Centre,
Reference
1 Vaidya J S, Mittra I. Fraction of normal remaining life span:
a new method for expressing survival in cancer. BMJ 1997;
314:1682-4. (7 June.)
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