Human Health And Disease

Healthy cells exhibit a property called contact inhibition, by which physical contact with neighbouring cells halts their further division, ensuring that tissues do not overgrow. In cancer cells this regulation breaks down, so they keep dividing uncontrollably to form a mass of cells called a tumour; malignant tumours can further invade surrounding tissues and spread to distant sites through the blood, a phenomenon known as metastasis. Apoptosis induction is incorrect as a description of the lost property, because apoptosis is programmed cell death; in fact cancer cells often evade apoptosis, but the specific feature lost that allows boundary-less division is contact inhibition. Active transport is wrong because it is a membrane process moving solutes against a gradient using ATP and is unrelated to the control of cell division. Osmoregulation is incorrect since it refers to maintaining water and salt balance in the body, having nothing to do with tumour formation. As discussed in NCERT Class 12, Chapter 8 (Human Health and Disease), oncogenes and carcinogens can transform normal cells into cancerous ones. As a biological consistency check, only the loss of contact inhibition directly explains why cancer cells ignore neighbour signals and proliferate without limit.