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Types of Cancer

           While cancer is not a single disease entity all forms of cancer share the common feature of growth dysregulation where the cells grow and multiply without restraint. Thus cancers can arise from all sites of the body and the number of cancers is equal to the number of types of cells and tissues we have in our body. It is estimated that there are 200 different types of cells the human body - all of which can potentially grow into a cancer. Further cancers can behave differently even when arising out the same type of cells in the same area of the body depending on their biological characteristics. For example in case of brain tumors low grade and high grade gliomas are considered to originate from the same cell type in the same area but have dramatically different prognosis. Recent research also indicates that cancers may be different depending the different molecular pathways that are deranged in them allowing far greater variability than originially anticipated.

       However for the purposes of easier treatment selection and classification cancers are broadly classified into the following categories depending upon the type of tissue of origin.

a) Carcinomas: These are the commonest types of cancers that arise from lining layers of cells (also known at the epithelium) covering the body and the organs. Epithelial cells have a natural tendency to grow and shed as they cover and protect the various organs, which in turn accounts for their propensity for developing into a cancer. Examples of common carcinomas include skin cancer, head neck cancers, lung cancers, breast cancers, prostate cancer, rectal cancer. Noteworthy is the fact that tobacco and alcohol use have a strong association with the development of nearly all types of carcinomas. As carcinomas arise in the cells lining the organs they are often detectable more easily and therefore several screening methods can be employed for early detection and diagnosis. For example Pap smears enable screening for cervical carcinomas and colonoscopies are effective in the screening for colo-rectal carcinomas. Carcinomas are typically categorized further according the site of origin for example the oral cavity, cervix, colon, rectum etc.

b) Sarcomas: These are cancers which arise from the supporting connective tissue, muscles, fat, bones in the body. Unlike the carcinomas these are typically more slow growing tumors and situated outside an organ. However since all organs in the body have a layer of connective tissue that supports the epithelial cells sarcomas can be found in all organs in the body. Further there are various forms of sarcomas with different growth potential that can arise from the same organs. However most of the sarcomas are slow growing tumors that require surgery as a part of the treatment. Unlike carcinomas smoking and alcohol abuse have not been shown to have a strong association with most of the sarcomas. Sarcomas are typically classified on the cell of origin rather than the site of origin.

c) Lymphomas/Leukemias: Unlike the other types of cancers mentioned above leukemias and lymphomas are cancers arising from the cells circulating in the blood stream. Leukemias are typically considered as "liquid tumors" as there is no single mass of cancer anywhere in the body but instead the malignant cells cirulate throughout the body. Leukemias are typically seen in young children and have become the model for curable cancers recently through the use of intense chemotherapy schedules along with the judicious use of radiation therapy. While lymphomas also arise from the blood forming cells they usually present with localized masses or tumors that can be seen. Like leukemias these are sensitive to radiation and chemotherapy both of which are important parts of the curative treatment. Recently molecular targetted agents have been used along with the traditional treatment for increasing the cure rates and survival. Lymphomas are classified as per the cell of origin unlike the carcinomas. Recently molecular diagnostic methods have been employed to classify these on the basis of the genetic mutations underlying the development of the cancer.

         While the above classification has the merit that it neatly categorizes malignancies into 3 categories with distinct approaches to management exceptions are known to occur. The art and science of treating cancer relies in the timely recognition of these atypical senarios and instituting the appropriate management. As a rule of the thumb surgery along with radiation therapy are the mainstay for the treatment of carcinomas and sarcomas while chemotherapy and radiation therapy play the major role in the treatment of leukemias/lymphomas.


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