CANCER

A neoplasm is an abnormal tissue that grows beyond normal cellular control mechanisms. It may involve almost any tissue in the body and may be benign or malignant, when it is referred to as a cancer. Most neoplasms are multifactorial. A small percentage with neoplasms have a strong predisposition that is inherited as a simple Mendelian trait. Some chromosome abnormalities are associated with an increased frequency of some malignancies. Two classes of genes are believed to be involved in the neoplastic process. They are Oncogenes and tumour suppressor genes. Oncogenes are normal genes that when altered, inappropriately expressed or overexpressed can lead to neoplasia. They are part of the normal genome and remain as proto-oncogenes or c-oncogenes, and do not cause cancer.

When activated, they change to the cancer causing oncogene. The development of chronic myeloid leukemia is such an example. Tumour suppressor genes function to prevent the development of neoplasms and a change in both the alleles and a conversion to a recessive active homozygous state, makes it acquire the cancer producing capability. The Retinoblastoma genes are an example. The p53 gene, which is involved in many cancers, particularly breast cancer is another example. The breast cancer genes BRCA1, BRCA2, and BRCA3 also belong to this category.