Title: “Inherited Cancer”
Adult onset cancer is a function of age, which means that we all have a probability to contract cancer each year we live. This probability varies with gender and age and is influenced by environmental factors. From the previous belief that cancer was caused by growth-genes (oncogenes), it was clarified that these genes could not be better functioning than when normal, the problem was the regulatory systems turning them on and off. In short, the problem is that growth genes has to be turned off to control cell growth. These downregulating genes are referred to as supressor genes. With very few exceptions, inherited cancer is in-borne defects in supressor genes, with the consequence that cellular growth is not downregulated and cellular growth becomes out of control, which is the cause of a tumour leading to cancer. The consequence is that persons born with such genetic defects have a higher probability per year to contract cancer. In early embryonic life cells are destined to become different types of tissues, and all their offspring cells will have all other genetic information made unavailable. The different tissues are using different systems of supressor cells to regulate cell growth. In consequence, inborn errors in given supressor gene will have different impact on cancer probability in different organs. When an organ is dependent on one system and have no very good back-up mechanism if this system fails, the person with a genetic inborn defect in that system will have an increased risk of cancer in that organ. The BRCA1/2 genes, despite being functional in all our cells every day, this way increase the risk for breast cancer and ovarian cancer when deranged. In contrast, the mismatch-repair genes MLH1, MSH2 and MSH6 – despite being instrumental in all our cells every day – increase the probability for gastrointestinal and gynaecological cancer when deranged.