Cancer occurs when mutations occur in genes that regulate cell division, leading to cells dividing without control.

A tumour is a mass of abnormal cells that have grown uncontrollably.

1. Benign tumours grow slowly, while malignant tumours grow rapidly, and can spread.
2. Benign tumours are surrounded by a capsule, while malignant tumours are not and so grow projections into surrounding tissue.
3. Benign tumours are non-cancerous and unlikely to be fatal, while malignant tumours are cancerous and more likely to be life threatening.
4. Benign tumours can usually be removed with surgery, while malignant tumours usually need radiotherapy and/or chemotherapy.

Primary tumours are the original abnormal growths that develop where a cancer first begins.

Secondary tumours are formed when primary tumours spread to other regions of the body via metastasis.

Oncogenes are mutated proto-oncogenes that can cause cells to divide uncontrollably and form tumours.

Oncogenes can be activated by mutations that cause constant cell receptor activation or excessive growth factor production.

Proto-oncogenes stimulate cell division when growth factors bind to a cell's receptors, activating DNA replication.

Tumour suppressor genes regulate cell division, repair DNA, and initiate apoptosis to prevent tumour formation.

Mutated tumour suppressor genes can become inactivated, leading to uncontrolled cell growth and cancer.

For example, the TP53 gene codes for the p53 protein, which is involved in DNA repair and apoptosis to prevent cancer. When it mutates, cells with damaged DNA continue to divide, leading to cancer.

Hypermethylation can silence tumour suppressor genes, resulting in increased cell division and tumour growth.

Hypomethylation can activate oncogenes, leading to excessive cell division and tumour formation.

Increased oestrogen levels can trigger breast cancer by activating genes controlling cell division, promoting transcription of these genes. This increases the rate of cell division within breast tissue and could lead to the development of a tumour.

There is a higher risk of breast cancer in postmenopausal women because they have higher levels of oestrogen production in fat cells within breast tissue.