| Ch 14 | Page 10 / 21 | |
| Cancer follow-up |
Expressing results | |
The aim of every treatment is to cure the largest number of patients.
Every man is going to die.
Cancer generally occurs during the second half of life or later, cure can be defined as the same life expectancy for a patient treated for cancer as a person of the same age and sex not affected by cancer.
Survival is the standard criteria of cancer treatment. It is generally studied through the calculation of survival curves, which is an estimation of the probability for a given subject to be alive at different times after the discovery of cancer.
Survival curves have three major aims:
Survival curves describe a group of subjects with a certain type of cancer.
A rapidly falling curve characterises a severe cancer (for instance, oesophageal cancer), whereas a curve becoming flat characterises more benign cancers, either spontaneously or after treatment.
For each time t (after cancer discovery), the probable disease evolution can be described according to the slope.
Some tumours rapidly develop with a steep slope, but then the slope becomes horizontal. This plateau represents the proportion of patients who will survive from their cancer. At that time, almost all living patients will survive from their cancer and follow-up procedures can be spaced out.
On the contrary, certain curves fall without any plateau, implying either continuous occurrence of relapses or the complete absence of remission.
The knowledge of survival curves for a group of patients enables to predict the statistical risk for the patient we are treating. Treatment intensity can therefore be adapted to mean prognosis.
However, when the patient wishes to discuss his/her chances to be cured, the true response is either 100% (total recovery) or 0% (death). Thus, giving percentages to a patient or to his/her family is of no meaning; this is particularly true at the beginning of treatment when we have no knowledge of how the cancer will respond
At the very best, this knowledge may help to temper excessive optimism and fanatic encouragements or stimuli on the part of patients or their families when prognosis is sombre (for example less than 10%), or, on the contrary, to stimulate patients into accepting treatment (even if toxic) when prognosis is relatively favourable (40-50% survival at 5 years) to favourable (> 70%).
Survival is the most objective criteria.
Comparison of curves, with all their statistical considerations, offers knowledge on disease characteristics which constitutes an important prognostic factor, and offers the proof that one treatment modality is better than another.
However, in this field, statistics should always be tempered by clinical good sense.
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