Cancer: A Terminal Disease - Essay Example

Cancer: A Terminal Disease Cancer is known to be terminal disease of mankind and responsible for death of in three woman and 1 in two men in USA. In present scenario, cancer research is getting maximum funding from all major funding agencies like , National Cancer Institute, USA, NIH, NSF, and UNESCO etc. (2) Similarly, private pharmaceutical companies are spending millions of dollars for development of drug against cancer. Unfortunately, the diehard effort and the money spending have lead to marginal progress in cancer treatment. Sometimes, scientist and researchers also wonder whether, are they moving on the right track to find a cure for cancer Only visible progress is observed in case of breast cancer even though, it is detected in early stage (3). There are many reasons and characteristic of cancer which makes it incurables some of them are as follows: 1) Complex interaction of genetic and environmental influence on cancer: Most of the human diseases were classified under two broad category; 1) genetic diseases and 2) environmental diseases. In genetic diseases mutation or loss of function in any of the vital gene leads to disease condition and they are generally cured by artificial supplementation of vital component. For example, in sickle cell anemia where patient having mutation in both copy of hemoglobin gene leads to sickle shaped RBC. The only permanent cure for this disease is bone marrow transplant and gene therapy, both of the techniques are in their nascent stage. While diseases like infection or normal injuries are environmental influence diseases and there are several treatments are available. In case of cancer both environmental as well as genetic factors plays important role and there is always arguments for more pronounce effect. For example in case of genetic factors there are many identified oncogenes (cancer causing gene) like RAS, EGFR, Myc etc. In normal cells they are part of cell cycle regulation (proto-oncogenes) but once get mutated they interfere with normal cell cycle and leads to uncontrolled growth or cancer. While environmental influence comes in the form of carcinogens (cancer causing chemicals). Tobacco, many organic solvents and chemicals, Ionizing radiation and UV radiation etc are consider to be most influential agents in causing cancer. Similarly, many epidemiological studies indicate life style, food habits and day to day routine also may leads to cancer. In spite of huge amount of data indicating role of above mention factors in cancer there is not a single case where any of these factors played role in isolation. It means there is always multifactor which leads to cancer and identification of all of these are almost impossible. Hence, the biggest challenge in front of cancer treatment is identification of causative agent and than targeting it. The complexity of causative agent and mulitifactorial influence has made cancer an incurable disease. 2) Systemic nature of Cancer : In early stage of cancer or malignancy the tumor is generated at particular location and if it is detected at this stage, then cure is possible in most of the cases. But, once the tumors start spreading (metastasis) than it is beyond therapeutic reach. For localize tumor surgical removal and subsequent radio or chemo therapy makes cancer curable but once metastasis started surgical removal of tumor is ruled out. Similarly, toxic side effect of whole body radiation and higher dose of chemotherapy leads to many unwanted complication and in most of the cases those side effects are more catastrophic than cancer it self. In conclusion, one can treat cancer if it detect in early stages and the tumor is localized but once it start spreading than it is impossible to cure it. 3) Treatment : A causative agent for cancer: In present day the two most widely used treatment procedure for cancer treatment is Radio therapy and chemotherapy. In both cases therapeutic agent itself can induced cancer. In radio therapy, high energy nuclear radiations are used to kill tumrous cells but the same radiation is consider being a major causative agent of cancer and hence any miss calculation in dose calculation may leads to induction of other kind of cancer. Similarly most of the chemotherapeutic agents interferes with basic metabolic activity of cells like DNA replication and hence may leads to induction of mutation and hence cancer. The very important factor of this treatment procedure is non-specificity. Here, killing of tumor cells occurs along with killing of normal cells makes these treatments limited to lower concentration or doses which in most of the cases become deciding factor for permanent cure of cancer. 4) Cancerous cells and normal cells are identical except growth: The major obstacle in treatment of cancer is identical nature of cancerous cells and normal cells. Metabolically and physiologically both types of cells are almost identical except the growth of malignant cells are exceptionally high than normal cells but this difference is not always sufficient to target malignant cells. Treatment like chemotherapy and radio therapy can not distinguish between two types of cells and hence cytotoxic effect exerted on both the type of cells leads to extensive killing of normal cells along with cancerous cells. This factor limits treatment of cancer, as even though there are many effective drugs are available in market it can not use due to non specific nature of drug. In recent past there are some development in area of targeted drug and novel drug delivery systems but that is in its native stage and not in treatment domain. 5) Development of drug resistance in cancerous cells: Cancer cells developed resistance to chemotherapeutic agent by various means like mutation and over expression of Drug target, enzymatic inactivation of drug. Efflux mediated elimination of drug from cells etc. this phenomenon is mainly observed in case of recurring tumors after initial chemotherapy. Fig 1 shows various proposed model for drug resistance. Drug resistance becomes prominent factor where anti cancer treatment fails and various approaches were taken to avoid it. For example inhibiting growth factor mediated resistance by controlling secretion of growth factors by cancer cells. But the limitation is prevalence of different mechanism of resistance and identification of that mechanism in particular case. Now day's therapist has hypothesized one of them and also has started the treatment or in most of the cases multiple drugs are administered for treatment thus, if cells are resistance to one drug can be eliminated by other. But, the biggest disadvantage of this approach is admission of higher dose leads to many unwanted side effects and hence limited to terminal cases of cancer where all other means got failed. Figure 1 Mechanism of Drug resistance in cancer cells (1) a | In the conventional model of tumour-cell drug resistance, rare cells with genetic alterations that confer multidrug resistance (MDR) form a drug-resistant clone (yellow). Following chemotherapy, these cells survive and proliferate, forming a recurrent tumour that is composed of offspring of the drug-resistant clone. b | In the cancer-stem-cell model, drug resistance can be mediated by stem cells. In this model, tumours contain a small population of tumour stem cells (red) and their differentiated offspring, which are committed to a particular lineage (blue). Following chemotherapy, the committed cells are killed, but the stem cells, which express drug transporters, survive. These cells repopulate the tumour, resulting in a heterogeneous tumour composed of stem cells and committed but variably differentiated offspring. c | In the 'acquired resistance' stem-cell model, the tumour stem cells (red), which express drug transporters, survive the therapy, whereas the committed but variably differentiated cells are killed. Mutation(s) in the surviving tumour stem cells (yellow) and their descendants (purple) can arise (by mechanisms such as point mutations, gene activation or gene amplification), conferring a drug-resistant phenotype. As in model a, the stem cell with the aquired mutations could be present in the population before therapy. d | In the 'intrinsic resistance' model, both the stem cells (yellow) and the variably differentiated cells (purple) are inherently drug resistant, so therapies have little or no effect, resulting in tumour growth. Conclusion: Cancer is one of the most investigated diseases in human kind and in spite of the priority area of research we don't have full proof cure for this disease. The only cure is early detection and prevention (4), but there was no therapeutic cure for the same. What we have achieved yet is the identification of some causative agent which may or may not be responsible for cancer in all the cases and therapy by which life of patient can be extended for few years. The biggest limitation of cancer research is probabilistic nature of causes and there is no deterministic explanation for the same. For example, smoking is consider being major factors for development of cancer but all smokers will not have cancer for life time but many non smokers have cancer. The reason behind this anomaly is complex interaction between genetic make up of individual and environment and till we don't have sound knowledge of this phenomenon and interaction we can not come up with cure of cancer. Similarly, metastasis nature of tumors makes it almost incurable as one can remove the tumor if it localized but one can not remove it form entire body. Almost identical nature of cancer cells and normal cells make it more difficult to develop targeted drug therapy which specifically eliminate cancer cell while normal cells remain unaffected. In conclusion there are miles to go ahead before we can cure the cancer and in present scenario except early detection, development of cancer can be slow down and hence life of patient get extended but can not be cure completely. Reference: 1) Tumour stem cells and drug resistance, Michael Dean, Tito Fojo & Susan Bates Nature Reviews Cancer 5, 275-284 (April 2005) 2) Cancer Research Funding, National Cancer Institute Fact sheet, April 19 2008, < http://www.cancer.gov/cancertopics/factsheet/NCI/research-funding> American Cancer Society Guidelines for the Early Detection of Cancer, 2005 Robert A. Smith, PhD, Vilma Cokkinides, PhD and Harmon J. Eyre, MD Cancer J Clin 2005; 55:31-44 http://www.cancer.gov/ Read More