Characteristics of Cancer - Coursework Example

Characteristics of Cancer Outline: -Introduction -Nomenclature and ification of Tumors -Malignant tumors -Benign tumors -Clinical manifestations-Carcinogens and their implications on society -Types of carcinogens -Conclusion -Bibliography Introduction: Cancer is a collection of diseases which are characterized by uncontrolled and abnormal growth and spread of cells. Inability to control this spread results in death eventually. Cancers are a multi-causal phenomenon that exist in our society. Not only are they affected by genetic factors which includes hormonal, mutational and immuno-causal factors but also by a variety of external factors which are social, sociological and societal, namely such as drinking, smoking and chemicals that are used in the production of the various products in our households. All these risk factors are collectively known as “Carcinogens” or Cancer-causing agents. They may act individually or together and start or play a role to the initiation of a series of events in the cells which would lead to a ‘Neoplasm’ in eventuality. A neoplasm is an abnormal mass of tissue whose growth, compared to normal tissues, is much faster and erratic and continues in the same fashion even after all stimulus is stopped. These neoplastic cells continue to multiply, independent of any physiological growth regulated stimulus and doing so, they increase in size and number, and usurp the nutrition of the cells in that region, causing complications. They are classified as benign or malignant based on their physiological interaction on the cellular level and have different approaches to their treatment. The nature of this disease is such that it may take up to ten years from exposure to detection for a particular type of cancer. Cancer is a leading cause of death worldwide: it accounted for 7.6 million deaths (around 13% of all deaths) in 2008. Lung, stomach, liver, colon and breast cancer cause the most cancer deaths each year. It has been the second highest cause of mortality in the United States, below cardiovascular diseases. Although medical science has made many strides in the field of oncology and most cancers can now be treated by a number of different approaches including surgery, chemotherapy, hormone therapy, radiotherapy and targeted therapy, it has failed to contain the spread of this disease due to lack of social awareness and unhealthy lifestyles that govern the incidence and epidemiology of this disease, particularly in the developing and poor countries. Therefore, there is a significant influence of environmental, geographical and sociological factors upon the growth and development of cancers in our societies. Classification & Nomenclature of Tumors There are a number of approaches to classify tumors. These include: i) Behavior ii) Appearance iii) Tissue of origin iv) Degree of differentiation Tumors are primarily classified as Benign or Malignant, however they have certain componential similarities, namely the parenchyma, which is made up of transformed cells and the stroma, which consists of connective tissue, blood vessels and inflammatory cells taken over from the host. It is from the parenchyma where the biological behavior and name of the tumor is determined. The Stroma plays a vital role in the growth and eventually sustains the development of the parenchymal cells. Malignant Tumors: Malignant tumors are those that can spread from their origin to multiple sites in the body to cause death. The process of proliferation is known as ‘Metastasis’ and is a defining characteristic of this type of tumor. Not only do they metastasize (bone sarcomas), but malignant tumors are also highly invasive (basal cell carcinomas and primary CNS tumors). Metastasis is a step by step process: 1. Growth and development of blood vessels of primary tumor. 2. Invasiveness and infiltration of basement membranes into blood or the lymphatic system 3. Successful transport and survival of tumor cells during circulation 4. Reaching the target tissue and passing across their basement membranes 5. Bypassing the defense mechanisms of the target tissue 6. Metastatic implant development Malignant tumors have three pathways of spreading: 1. Lymphatic (Carcinomas) 2. Hematogenous ( Sarcomas) 3. Seeding within cavities of the body (ovarian cancers) They also have variation in the aggressiveness of their spread, and a wide degree of parenchymal cell differentiation which makes their identification difficult and therefore have to be treated accordingly. Compared to their benign counterparts, malignant tumors that have cells that are undifferentiated are identified as Anaplasic, broadly speaking, this refers to cells exhibiting a loss of functional and morphological differentiation which would be otherwise present in normal cells. Such cells also exhibit Pleomorphism i.e. clear variation in shape and size. They have nuclei which are large and hyperchromatic and can be clearly identified by their dark stain. An increased nuclear-cytoplasmic ratio together with abnormally large nucleoli and chromatin that is thick and clumped is observed. It is interesting to note that they also have an abnormal mitotic process in which multiple anarchic spindles are observed, particularly in quadripolar and tripolar forms. A greater degree of anaplasia corresponds to a more aggressive tumor whereas a well differentiated tumor indicates a less aggressive tumor. A. Carcinoma is a malignant tumor that manifests in the epithelium and has multiple variations. These include: i) Squamous cell carcinoma: They are identified by their distinct production of Keratin and are found in the stratified squamous epithelium of the mouth, skin, and vagina and in the regions of squamous metaplasia, particularly in the squamocolumnar junctions of the uterine cervix and in the bronchi. ii) Transitional cell carcinoma: They develop in the transitional cell epithelium of the urinary tract. iii) Adenocarcinoma: They are particularly found in the glandular epithelium and therefore include tumors of the mucosal layer of the gastrointestinal region, the endometrium and the pancreas. Often found in correlation with the tumor-induced spread of non-neoplastic fibrous connective tissue, namely in the adenocarcinoma of the prostate, breasts and the pancreas, which is otherwise known as Desmoplasia. B. Sarcoma: It is a tumor that has its origins in the mesenchymal layer. Different manifestations include Osteosarcoma (bone), rhabdmyosarcoma (skeletal muscle), leiomyosarcoma (smooth muscle) and liposarcoma (fatty tissue). C. Teratoma: It is a neoplasm which is composed of different tissue types, usually the three germ layers, none of which are present in its region of occurrence. Usually found in the ovaries or testis. D. Eponymous tumors: Namely Burkitts lymphoma, Hodgkin disease and Wilms tumor. Benign Tumors: Benign tumors are characterized by their slow growth and lack of metastasis in contrast to malignant tumors, similarity to the tissue of their origin and a great degree of differentiation. Upon observation they are noted to show encapsulation. A. Papilloma: This is an epithelial neoplasm which presents itself as a protrusion from the surface epithelium, in cases of squamous epithelium of the tongue and larynx or from transitional epithelium, of the urinary bladder, ureter or pelvis. A characteristic feature is the presence of fine finger-like epithelial protrusions which layer a centre of connective tissue stroma which contains blood vessels. B. Adenoma: This is a tumor of the glandular epithelium which has further sub-types: i) Papillary cystadenoma: A tumor identified by the presence of adenomatous papillary protrusions into spaces present in the cysts. Occurs in the ovaries. ii) Fibroadenoma: Distinctly identified by the increase in the connective tissue that covers the glandular epithelium. Occurs in the breasts. C. Mesenchymal benign tumors: These are named in accordance of the tissue in which they originate. Examples include leiyomyomas, fibroid tumors, lipomas and chondromas. D. Choristoma: These are minute non-neoplastic regions of normal tissue present in an abnormal location, such as the presence of pancreatic tissue in the stomach wall. E. Hamartoma: An overgrowth of mature cells in an affected organ, characterized by their disorganization and a prominent expression of a particular characteristic. E.g. An irregular accumulation of blood vessels. Clinical Manifestations: There are certain characteristics of cancers that are governed by mechanisms other than metastasis and invasion. A. Cachexia and muscle wasting: Includes weakness, loss of weight, anemia, infection, anorexia and an abnormally increased metabolism. Could be mediated by Cachectin. B. Endocrine abnormalities: Abnormal hormonal activity which results in a number of syndromes caused by the presence of a tumor in the endocrine glands. Subtypes include: i) Pituitary abnormalities ii) Adrenocortical abnormalities iii) Ovarian abnormalities iv) Trophoblastic tissue abnormalities C. Paraneoplastic syndromes: A collection of signs and symptoms which are developed as a consequence of either the presence of the tumor or substances being released by it. i) Endocrinopathies: Cushing syndrome, Hypercalcemia, Hypoglycemia, Hyperthyroidism. ii) Neurological abnormalities: Dementia, Peripheral neuropathies. iii) Skin lesions: Acanthosis nigricans and dermatomyositis. iv) Coagulation abnormalities: Migratory thrombophlebitis, Trosseau phenomenon. D. Oncofetal antigens: Include proteins like the Alpha fetoprotein (AFP) and Carcinoembryonic antigen which are associated with Hepatocellular carcinomas and Colon cancers respectively. Usually only expressed during embryonic life. Carcinogens and their implications on society Carcinogens or ‘cancer-causing’ agents are both endogenous and exogenous. The tumor formed is a consequence of the interaction between a person’s DNA and the agent and the resulting processes that follow. It is true that genetic damage rests at the core of all cancers, however, epidemiological and etiological studies have made it clear that it is the environmental, social and societal risk factors which play a major role in the spread and growth of cancers in modern day society and if these are either eliminated or their pervasiveness restricted through preventative methodologies, early detection and treatment, and proper education and management, results could be otherwise. This is also supported by the geographical variation of the different forms of cancer. For example, compared to Japan, death rates from breast cancer are higher in the US and Europe by four to five times, whereas the death rates for stomach carcinoma is seven times higher in Japan than in the US. “About 30% of cancer deaths are due to the five leading behavioral and dietary risks: high body mass index, low fruit and vegetable intake, physical inactivity, tobacco use, alcohol use and hence are preventable. According to the World Health Organization, the main types of cancers are: lung (1.4 million deaths) stomach (740 000 deaths) liver (700 000 deaths) colorectal (610 000 deaths) breast (460 000 deaths). About 70% of all cancer deaths occurred in low- and middle-income countries. Deaths from cancer worldwide are projected to continue to rise to over 11 million in 2030.” (WHO) Types of Carcinogens: A.Chemicals i. Direct-reacting carcinogens do not require any sort of chemical alteration to react. ii. Indirect-reacting carcinogens undergo a metabolic transformation from Procarcinogens to active Ultimate carcinogens. They include chemicals present in various scenarios like Alkylating agents, benzene, PVC, arsenic; metals like asbestos, uranium, nickel, chromium, which are classified as risk factors of occupational cancers and social behavioral habits like cigarette smoking, hookah smoking, alcohol, a sedentary lifestyle resulting in obesity, and unhealthy dietary habits like a high fat diet or a low fiber diet. “Tobacco use is the single most important risk factor for cancer causing 22% of global cancer deaths and 71% of global lung cancer deaths.” (WHO) As for risk factors like obesity and unhealthy dietary habits, incorporation of a moderate amount of fruits and vegetables together with a little physical activity drastically lowers the risks associated with cancer and even cardiovascular diseases.  A relation has been found between obesity and many types of cancers such as oesophagus, colorectum, breast, endometrium and kidney. B. Radiant energy Excessive ultraviolet radiation from sunlight correlates to the frequency of basal cell, squamous cell carcinomas and melanomas. Ionizing radiation is another typical carcinogen and people exposed to it have been afflicted by a number of diseases such as lung cancer in uranium miners, skin cancer and myeloid leukemias in radiologists, osteosarcoma in radium watch dial workers. A prominent example is the death of the Nobel Prize winner Marie Curie who died of leukemia. “Residential exposure to radon gas from soil and building materials is estimated to cause between 3% and 14% of all lung cancers, making it the second cause of lung cancer after tobacco smoke” (WHO) C. Microbial agents They include: -Viruses: i) DNA viruses integrate their DNA into host cell genomes which results in an expression of viral mRNA coding for certain proteins. Examples include HPV, Epstein-Barr virus and HBV. “Cancer causing infections such as HBV and HCV, HPV are responsible for 20% of cancer deaths in low and middle income countries and 7 % in high income countries.” (WHO) ii) Retroviruses are characterized by the action of viral reverse transcriptase transcribing viral genomic RNA sequences into DNA. -Viral Oncogenes - Oncogenes “Infectious agents are responsible for almost 22% of cancer deaths in the developing world and 6% in industrialized countries.” (WHO) Conclusion: In light of the statistical data brought forward by the various health organizations, we can ascribe importance to the fact that the sociological, geographical and social factors play a great role in the large number of deaths caused globally by cancer per year and long lasting efforts need to be made in order to prevent, manage and cure cancer patients, perhaps by bringing changes to the different societal systems by educating people about the various aspects of the carcinogens that they come in contact during daily life, by developing better screening tests to detect and contain the spread of the disease before hand. Bibliography: American Cancer Society. Cancer Facts & Figures 2011. Atlanta: American Cancer Society; 2011 Dorland, W A. N. Dorlands Pocket 28th edition Medical Dictionary. Philadelphia: Saunders, 1995. Print. Kumar, Vinay, Abul K. Abbas, Nelson Fausto, Stanley L. Robbins, and Ramzi S. Cotran. Robbins and Cotran Pathologic Basis of Disease. Philadelphia: Elsevier Saunders, 2005. Print. Schneider, Arthur S, and Philip A. Szanto. Pathology. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2009. Print. (WHO, Cancer Fact sheet N°297) (WHO) Read More