Principles Of Cancer Treatment Curability

The logical objective of the treatment of cancer is destruction of all cancer cells. The disease is then eradicated and the patient 'clinically cured'. This definition of clinical cure is impractical as it can only be proven by a complete search for asymptomatic deposits of tumour on death. However, clinical cure should follow the complete removal of all non-invasive cancers, and also a number of small invasive cancers, particularly in superficial sites, which have not metastasized.

Life is personal and freedom from recurrence of the cancer during the remainder of a patient's lifetime constitutes 'personal cure'. This does not rule out the possibility that the disease is present in asymptomatic form and is clearly dependent upon the duration of life following its diagnosis. By this definition, the patient who is killed in a road accident on the way home from hospital following the palliative resection of an incurable gastric cancer is 'cured'!

A third definition of cure is 'statistical cure'. Those achieving such cure form a group of disease-free survivors whose annual death rate from all causes is the same as that of a group of the normal population of similar sex and age distribution. The time at which they can be expected to be statistically cured depends on the natural history of the disease. For aggressive cancers such as those of lung, few patients will survive for >5 years, whereas for those which are chronic, excess mortality from metastatic disease may persist for >30 years (Fig. 9.15). Only if the disease is aggressive and rapidly progressing can 5-year survival rates be regarded as a valid index of cure.

Whichever definition of cure is used, the objective of treatment is to cure the disease. Traditionally the only hope of curing a cancer is to 'cut it out'. With the discovery of anaesthetics, antiseptic and later aseptic surgery, operations became more extensive, partly on account of the advanced

Years

Figure 9.15. Mortality curves for some common cancers.

Years

Figure 9.15. Mortality curves for some common cancers.

stage at which many tumours presented to surgeons, but also because it was believed that there were two distinct stages in the natural history of a cancer: a 'primary stage' when the cancer is confined to its organ or other site of origin and their regional lymphatics, and a 'secondary stage' when it is disseminated to distant sites. Only when the natural defences of the lymph nodes draining the primary site is overridden was such secondary spread believed to occur. Haematogenous spread was regarded as a late phenomenon. This concept has been replaced by evidence that invasive cancer disseminates early in its course by both lymphatic and blood systems to form micrometastases in regional lymph nodes and in systemic organs and tissues. Although it may be many years before these micrometastases become clinically evident, the effective treatment of invasive cancer now includes not only the control of local disease by surgery and/or radiotherapy but also of systemic disease by chemotherapy and, in a few hormone-dependent cancers, antiendocrine measures. The objective of systemic treatment is eradication of micrometastases.

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