Biology of Disease

is to extract DNA using a fine needle biopsy, to amplify the DNA by using

the polymerase chain reaction (PCR; Chapter 3), and to analyze the DNA

obtained for mutations known to be implicated in cancer. Fluorescence in situ

hybridization technique (FISH; Chapter 4) is also applied to diagnosis. Thin

sections of the tumor are treated to separate the DNA strands which are then

hybridized in situ with fluorochrome labeled probes for relevant mutated,

cancer associated genes (Figure 17.24). The slides are then examined using

a fluorescence microscope. The presence of the mutation is indicated by

fluorescent spots in the nucleus.

Figure 17.24Schematic to outline the binding

of a fluorescently-labeled DNA probe to target

specific chromosomal DNA sequences (FISH). The

use of FISH in the specific staining of telomeres is

shown in Figure 18.9.

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Excitation

light

Chromosomal DNA

Fluorescein labeled

DNA probe

Fluorescence

Fluorescence

Chromosome with

bound

fluorescent label

17.7 General Treatment of Cancer

The traditional treatment for primary tumors that have not metastasized to

other locations in the body has been surgical excision of the tumor, followed

by chemotherapy or radiation therapy (radiotherapy). Chemotherapy involves

the use of drugs to kill cancer cells while radiotherapy uses ionizing radiation.

However, where a tumor has been diagnosed in an advanced state with

metastases in other parts of the body, palliative care only may be given, to

ease pain and discomfort.

‘Staging’ of the cancer is essential as it determines the treatment that the

patient receives. Staging of a cancer involves looking at the extent of the

cancer within the body. Though staging varies between different types of

tumor, a simple system classifies the tumor into one of four stages as shown

inTable 17.6. Other staging systems include the TNM classification, where T

records how far the primary tumor has grown in its original location, N defines

whether the tumor has spread to local lymph nodes and M describes whether

the tumor has metastasized. The staging of cancers will be discussed further

inSection 17.8.

The aims of chemotherapy and radiotherapy are to stop the cancer cells from

dividing. Other treatments which have been attempted, with varying success

include immunotherapy, where the objective is to stimulate the body’s

immune system to eliminate the cancer, as well as a number of ‘alternative’

therapies all of which are controversial.