Which of the following is a characteristic of malignant tumour cells compared to benign tumour cells?

• They are surrounded by a thick, protective capsule of dense connective tissue.
• They have the ability to invade neighbouring tissues and metastasise to distant organs.
• They undergo cell division much slower than normal healthy somatic cells.
• They remain permanently localized at their original site of origin.

Some colorectal cancers are stimulated to grow when epidermal growth factor (EGF) binds to specific receptor proteins on their cell membranes. Explain why treating patients with monoclonal antibodies designed to block these EGF receptors can be an effective therapy.

Cells usually become cancerous due to mutations in genes regulating the cell cycle. Scientists have identified the APC gene, which normally acts as a tumour suppressor to prevent uncontrolled cell division.

In a population of $36400000$ individuals, $1$ in $650$ carries a pathogenic mutation in their APC gene.

• $95\%$ of individuals with this mutation will develop colorectal cancer if left untreated.
• Calculate how many individuals in this population could develop colorectal cancer due to this inherited APC mutation. Show your working.

Genetic screening allows individuals to discover if they carry the mutated APC gene. Carriers are often offered a prophylactic total colectomy (surgical removal of the entire large intestine) before cancer develops. Suggest two reasons why deciding to undergo this procedure can be extremely difficult for a carrier of this mutation.