Biology topic 8 : Tumours

What is a tumour?

Group of abnormal cells that form a lump or growth, arising from any body cell type

How can all tumours cause harm , even if not cancerous?

They can damage the organ they grow in, cause blackages or exert pressure on surrounding tissues

What is a malignant tumor?

C cancerous tumour that grows rapidly invades surroiunding tissues and can spread to other parts of the body

How do malignant tumors invade and destrory tissues?

They grow quickly and inflitrate neighbouring tissues, disrupting there normal structure and function

Why do malignant tumors stimulate blood vessel formation?

Their cells secret chemicals that trigger angiogenesis , supplying the tumour with oxygen , nutrients and growth factors

What is metastasis?

Process where malignant cells break off, travel through bloodstrem or lymphatic system, and form secondary tumours elsewhere

Why can malignant tumors grow back after surgery?

Becouse cancerous cells may remain or continue dividing uncontrollably allowing the tumour to reform

What factors can initiate malignant tumour formation?

Carciogens such as UV or X ray exposure, robacco smoke, asbestos an dprocessed meats

What is a benign tumour?

A non cancerous tumour that grows slowly and does not invade other tissues or metastasise

How can benign tumors still cause harm?

Causing blackages or pressing on organs and surrounding tissues, affecting their function

Do benign tumors grow back after removal?

They usually do not grow back becouse they do not invade surrounding tissue

What factors can initiate benign tumour formation?

Inflammation, injection injury, diet, genetic toxins, or radiation

What are examples of beign tumours?

polypus in the nose, colon, overies, non cancerous brain rumours, and warts caused by viral infections

How does cancer arise at the cellular level?

Cancer develops when mutations occur in genes that regulate the cell cycle causing uncontrolled mitosis and the formation of a tumour

Whyd do mutations in cell - cycle genes increase cancer risk?

Becouse they convert normal regulatory genes into oncogenes, leading to continuous cell division

Why dont most mutations lead to cancer?

Most mutations cause early cell death or are removed by the immune system and damaged cells are easily replicated

How can harmful mutations contribute to tumour development?

IF they escape repair or immune detection they are passed to all decendent cells, allowing abnormal growth to accumlate

What increases the likelhood of cancer causing mutations?

Exposure to carcinogens such as UV radiation, tabacco tar and Xrays

What do tumour suppressor genes normally do?

they repair DNAThey repari DNA , slow the cell cycle at checkpoints and trigger apoptosis when damage cannot be repaired

How can tumour suppressor gene failure lead to cancer?

Mutations or epigenetic silencing prevent the production fo proteins that control cell division , allowing abnormal cells to survive and divide

What is the role of BRCA - 1 tumour suppressor gene?

BRCA - 1 repairs damaged DNA or triggers apoptosis if repair fails, especially in breast tissue

How does reduced BRCA - 1 expression contribute to brest cancer?

Without BRCA - 1 DNA damage accumlates, increasing the liklihood of uncontrolled cell division

What are proto - oncogenes?

Normal genes that code for protines stimulating cell growth and differentiation

How do proto - oncogenes becomes oncogenes?

Mutations often cuased by carcinogens activate them permanently causing constant stimulation of cell division

How does oncogene activation affect the cell cycle?

It speed up the cell cycle by continusly activating growth - promoting protines

How can oncogene activation occur at the DNA level?

Through inversion or translocationmutation that increase gene expression or prevent the protine from being switched off

How does increased methylation of tumour suppressor genes promote cancer?

It silences the gene by preventing transcription factors binding, so tumour suppressor protines are not produced

How can siRNA contribute to tumour formation?

siRNAs targeting tumour suppressor mRNA causes its breakdown reducing tumour - suppressor protine levels

How does reduced methylation of proto-oncogenes promote cancer?

It increases gene accessibilty allowing transcription factors to bind and overactivate protine synthesis, making the gene behave like an oncogene

How does oestrogen influence gene expression?

Oestrogen binds to ERa receptors in the nucleus , activating transcription of genes that stimulate cell growth and replication

Why can high oestrogen levels lead to brest cancer?

Excess can overstimulates ERa dependent gene transcription, increasing cell division and tumour risks

What percentage of breast tumours aer oestrogen recptor - positive?

Around 70% of breast tumours express oestrogen receptors

How does tamoxifen inhibit oestrogen - dependent tumour growth?

Tamoxifen competitively binds to ERa receptors , preventing oestrgen from activating, transcription of growth promoting genes