Provide information about cancer,and explain the causes,detection,diagnosis,and treatment of cancer.

(A) Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. More than a million Indians suffer from cancer and a large number of them die from it annually. The mechanisms that cause transformation of normal cells into cancerous neoplastic cells,treatment,and control of cancer are some of the most intense areas of research in biology and medicine.
In our body,cell growth and differentiation is highly controlled and regulated. Cancer cells lose this property of control. Normal cells show a property called $contact$ $inhibition$ by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appear to lose this property. As a result,cancerous cells just continue to divide giving rise to masses of cells called $tumors$.
$Tumors$ are of two types: $benign$ and $malignant$. $Benign$ $tumors$ normally remain confined to their original location and do not spread to other parts of the body and cause little damage. $Malignant$ $tumors$ are a mass of proliferating cells called $neoplastic$ or $tumor$ $cells$. These cells grow very rapidly,invading and damaging the surrounding normal tissues. As these cells actively divide and grow,they also starve the normal cells by competing for vital nutrients. Cells sloughed from such tumors reach distant sites through blood,and wherever they get lodged in the body,they start a new tumor there. This property called $metastasis$ is the most feared property of malignant tumors.
$Causes$ $of$ $Cancer$: Transformation of normal cells into cancerous neoplastic cells may be induced by physical,chemical,or biological agents. These agents are called $carcinogens$.
Ionizing radiations like $X-rays$ and $gamma$ $rays$ and non-ionizing radiations like $UV$ cause $DNA$ damage leading to neoplastic transformation. The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer. Cancer-causing viruses called $oncogenic$ $viruses$ have genes called $viral$ $oncogenes$.
Furthermore,several genes called $cellular$ $oncogenes$ $(c-onc)$ or $proto-oncogenes$ have been identified in normal cells which,when activated under certain conditions,could lead to oncogenic transformation of the cells.
$Cancer$ $detection$ $and$ $diagnosis$: Early detection of cancers is essential as it allows the disease to be treated successfully in many cases. Cancer detection is based on biopsy and histopathological studies of the tissue and blood and bone marrow tests for increased cell counts in the case of leukemias.
In biopsy,a piece of the suspected tissue cut into thin sections is stained and examined under a microscope (histopathological studies) by a pathologist. Techniques like radiography $(X-rays)$,$CT$ ($computed$ $tomography$),and $MRI$ ($magnetic$ $resonance$ $imaging$) are very useful to detect cancers of the internal organs.
$CT$ uses $X-rays$ to generate a three-dimensional image of the internals of an object. $MRI$ uses strong magnetic fields and non-ionizing radiations to accurately detect pathological and physiological changes in the living tissue.
Antibodies against cancer-specific antigens are also used for certain cancers. Techniques of molecular biology can be used to detect genes in individuals with inherited susceptibility to certain cancers. Identification of such genes,which predispose an individual to certain cancers,may be very helpful in prevention of cancers. Such individuals may be advised to avoid exposure to particular carcinogens to which they are susceptible (e.g.,tobacco smoke in case of lung cancer).
$Treatment$ $of$ $Cancer$: The common approaches for treatment of cancer are surgery,radiation therapy,and immunotherapy. In radiotherapy,tumor cells are irradiated lethally,taking proper care of the normal tissues surrounding the tumor mass. Several chemotherapeutic drugs are used to kill cancerous cells.
Some of these are specific for particular tumors. Majority of drugs have side effects like hair loss,anemia,etc. Most cancers are treated by combination of surgery,radiotherapy,and chemotherapy. Tumor cells have been shown to avoid detection and destruction by immune system. Therefore,the patients are given substances called biological response modifiers such as $\alpha-interferon$ which activates their immune system and helps in destroying the tumor.