Cancer and its consequences

Published on 01/03/2015 by admin

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69

Cancer and its consequences

In Western societies one death in five is caused by cancer. The effects of tumour growth may be local or systemic (Fig 69.1), e.g. obstruction of blood vessels, lymphatics or ducts, damage to nerves, effusions, bleeding, infection, necrosis of surrounding tissue and eventual death of the patient. The cancer cells may secrete toxins locally or into the general circulation. Both endocrine and non-endocrine tumours may secrete hormones or other regulatory molecules.

A tumour marker is any substance that can be related to the presence or progress of a tumour (see pp. 140–141).

Local effects of tumours

The local growth of a tumour can cause a wide range of abnormalities in commonly requested biochemical tests. This may be a consequence of obstruction of blood vessels or ducts, e.g. the blockage of bile ducts by carcinoma of head of pancreas causes elevated serum alkaline phosphatase and sometimes jaundice. The symptoms that result from such local effects may be the first sign to the patient that something is wrong, but there may be no initial suspicion that there is an underlying malignancy.

The liver is often the site of metastatic spread of a tumour. An isolated increase in the serum alkaline phosphatase or γGT is a common finding when this occurs. Even with significant liver involvement, there may be no biochemical abnormalities. Modest increases in the aminotransferases, ALT and AST, are observed if the rate of cell destruction is high.

Metastatic spread of a tumour to an important site may precipitate complete system failure. For example, destruction of the adrenal cortex by tumour causes impaired aldosterone and cortisol secretion, with potentially fatal consequences.

Rapid tumour growth gives rise to abnormal biochemistry. Leukaemia and lymphoma are often associated with elevated serum urate concentrations due to the rapid cell turnover. Serum lactate dehydrogenase is often elevated in these patients, reflecting the high concentration of the enzyme in the tumour and the cellular turnover, and may be a sign of intravascular haemolysis. Large tumours may not have an extensive blood supply and the tumour cells meet their energy needs via anaerobic glycolysis. This may result in the generation of a lactic acidosis.

Renal failure may occur in patients with malignancy for the following reasons:

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