1. Point mutation

2. DNA amplification

3. Chromosome alterations.

Only chromosome alteration will be discussed in this article.

It is easy to see that chromosome changes may provide clues to genetic changes in cancer. Most chromosomal translocations have been observed on haematopoietic cancers. The breakpoints often occur at sites of cellular protooncogenes. Translocations are common in lymphoid tumours probably because these cells normally rearrange DNA to generate antigen receptors. Imperfect regulation of receptor gene rearrangement may be involved. An example is Burkitt's lymphoma, a B-cell tumour characterized by a reciprocal translocation between chromosomes 8 and 14.

Chromosomal alterations can lead to the abnormal expression of a transcription factor that performs its normal function and turns on growth-related genes. Gene rearrangements most commonly involve transcription factors. The first chromosomal abnormality detected in human malignancy was the Philadelphia chromosome in Chronic Myeloid Leukaemia. The consequence of this abnormality is the activation of signal transduction pathways leading to cell growth independent of normal external growth signals.

Technical obstacles have slowed the identification of recurring chromosomal alterations in human solid tumours particularly carcinomas because of the complexities of chromosome alterations in such tumours.