Lung cancer Tar in smoke contains several carcinogens (cancer causing agents) Cause mutations in the genes which control cell division (oncogenes) Divide uncontrollably to produce a mass of cells - tumour Tumour cells do not respond to signals from nerves and hormones Continue to grow No programmed cell death occurs A small group of tumour cells is called a primary growth. It may be Benign - does not spread from its origin Malignant - spread throughout the body invading other tissues and destroying them Cells breaking off malignant tumours from secondary growth cause cancer to spread - metastasis Hard to find and remove them in this state Tumour may take many years to develop with few or no real symptoms Well advanced when discovered If the respiratory system is involved: Symptoms like coughing up blood and blocked airways leading to diseases like pneumonia are common Removing a whole or part lung may be effective provided metastasis is not well advanced Smoking and lung cancer risk Risk increases if Smokers start young Inhale deeply More cigarettes are smoked per day The cigarettes are high tar Smoking goes on over a long period of time Risk decreases if smoking stops Smokers 18x more likely to develop lung cancer than non-smokers One third of all deaths from cancer can be attributed to smoking Genes and Cancer 3 types of evidence support a link Tendency to develop cancer seems to be inherited Tumour cells in some cancers have abnormal chromosomes There is a positive correlation between mutations and carcinogens Genes causing cells to become cancerous are called oncogenes (oncology = study of cancer) They are found when proto-oncogenes, normal versions of genes, mutate and become overactive The RAS proto-oncogene codes for plasma membrane proteins called G-proteins G-proteins enable cells to respond to growth factors These G-proteins are normally activated by one of their own enzymes GTPase The mutant ras gene produces GTPase deficient G-proteins / they remain active longer causing tumours Myc oncogenes (chromosome 8) Myc proto-oncogenes produce proteins needed for transcribing genes required for normal cell division Common mutation switches the myc proto-oncogenes to chromosome 14 where it acts as an oncogene / abnormal cell division / tumour When both ras and myc oncogenes are present together, malignant cells will result Tumour suppressor genes Associated with cell division Converted to oncogenes by mutation and reduce normal activity by inhibiting cell division Might inhibit transcription of the proto-oncogenes like myc May become overactive → tumour