Introduction:
Cells are the fundamental building blocks of the human body. Cells divide and grow to create new cells as the body requires them. Cells normally die when they become too old or damaged; then, new cells replace them. Cancer develops when genetic changes disrupt the orderly process. Cells begin to proliferate at an uncontrollable rate. These cells may combine to form a mass known as a tumor. A tumor may be malignant or benign. A malignant tumor can grow and spread to other body parts. A benign tumor can grow but does not spread. Some cancers do not produce a tumor. These include leukemias, lymphomas of various types, and myeloma.
What Is a Tumor?
A tumor is an abnormal mass of tissue. It is formed when the cells grow and divides more than they should or do not die when they should. It can be benign (not cancerous) or malignant (cancer). Benign tumors can grow in size but do not spread or invade nearby tissues or other parts of the body. Malignant tumors (cancer) can spread into or invade nearby tissues. Tumors can also spread to other parts of the body. It may spread via the blood and lymph systems (neoplasm).
What Is the Difference Between a Tumor and Cancer?
Cancer is a group of diseases. It is characterized by abnormal cell growth that can spread to other body parts. It is the leading cause of death in the world, accounting for approximately 10 million deaths in 2020, or one in every six deaths. A tumor is formed in the body when a lesion or lump develops due to abnormal cellular growth. It may be benign growth or malignant growth.
Benign tumor growth is restricted to a specific area of the body. When a tumor becomes malignant, it is called cancer. This means that primary growth can give rise to secondary growths, invading vital organs and spreading throughout the body. Depending on several factors, a tumor may or may not progress into cancer.
How Do Genetic Alterations Cause Tumors?
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A tumor is caused by a breakdown in the controls that regulate cell division. Changes in important genes are always among the causes of the breakdown. These changes are frequently caused by mutations, which are changes in the DNA (deoxyribonucleic acid) sequence of chromosomes.
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Mutations can be very small, affecting only a few nucleotides, or very large, causing major changes in chromosome structure. Cell behavior can be affected by both small and large mutations. A combination of mutations in important genes can cause a tumor.
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Most of the tumors occur from a single mutant precursor cell. As the precursor cell divides, the resulting daughter cells acquire mutations and behaviors over time. Cells with an advantage in division or resistance to cell death will tend to dominate the population. As a result of this the tumor cells can acquire a wide range of capabilities that are not normally seen in the healthy version of the cell.
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Mutations in key regulatory genes (tumor suppressors and proto-oncogenes) alter cell behavior and may contribute to the uncontrolled growth seen in cancer. The transition from a healthy normal cell to a cancer cell is a step-by-step process that requires many genetic changes.
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These mutations can be found in oncogenes as well as tumor suppressor genes. This is one of the reasons why cancer is much more common in older people. Many mutations must occur in a cell to develop into a cancer cell. The risk of several mutations occurring in the same cell is extremely uncommon because the likelihood of any gene becoming mutated is quite low.
What Are the Different Types of Gene Mutations That Lead to Tumors?
A variety of genetic alterations can cause tumors. It includes the following.
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Point Mutations - This mutation only affects a single nucleotide or DNA letter. It may result in the possibility for one nucleotide to be absent or for another nucleotide to take its place. Approximately 5 % of cancer patients have a point mutation in the KRAS gene, which replaces the DNA letter G with A. This single-letter change results in an abnormal KRAS protein and abnormal cell growth. Point mutations are again subdivided into nonsense, missense, and frameshift mutations.
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Chromosomal Rearrangements - Segments of DNA can be moved about, erased, or replicated, which can result in genetic alterations that can lead to cancer. A chromosomal rearrangement that positions a portion of the BCR gene next to the ABL gene leads to chronic myelogenous leukemias (blood cancer). The BCR-ABL protein is abnormally produced due to this rearrangement, which causes leukemia cells to proliferate out of control.
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Epigenetic Changes - Epigenetic changes influence how DNA is packed into the nucleus. These changes can alter how much protein a gene produces by changing how DNA is packaged. Epigenetic changes are reversible and do not affect the DNA code. Methylation and acetylation are two types of epigenetic changes.
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Translocations - These involve the breakage of DNA fragments and the movement of chromosome fragments. Breaks in two distinct chromosomes result in the formation of two new chromosomes with new gene combinations. Translocations are frequently found in leukemias and lymphomas but less frequently in solid tissue malignancies. Burkitt's lymphoma, B-cell lymphomas, and other leukemia subtypes are further malignancies that are frequently (or always) linked to certain translocations.
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Induced Mutations - Mutations can be induced when the cells are exposed to various procedures. It includes radiation, free-radical injury, chemical mutagens, and chronic inflammation.
What Are the Commonly Mutated Genes Linked to Hereditary Cancer Risk?
Inherited mutations are linked to different types of gene mutations and cancer. Some cancers are more likely to be inherited. The following is a list of common cancers and the most common genes associated with an increased risk.
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Pancreatic Cancer - BRAC1, CDKN2A, BRACA2, ATM.
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Breast Cancer (Women) - BRCA1, BARD1, BRIP1, ATM, CHEK2.
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Endometrial Cancer - MLH1, MSH2, BRACA1, MSH6.
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Melanoma - BAP1, BRCA2, CDK4, PTEN.
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Prostate Cancer - ATM, CHEK2, BRCA1, BRCA2, PALB2.
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Colorectal Cancer - APC, MSH2, MLH1, EPCAM, PMS2.
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Breast Cancer (Men) - BRCA1, CHEK2, BRCA2, PALB2.
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Gastric Cancer - APC, CDH1, STK11, EPCAM, MLH1, MSH2.
Conclusion:
Genetic changes can cause tumors by altering how the cells grow and spread. The majority of cancer-causing DNA changes occur in genes, which are sections of DNA that carry the instructions for making proteins or specialized RNA like microRNA. Several factors are responsible for inducing gene mutations in a living cell. DNA alterations can affect the function, structure, and production of corresponding proteins, resulting in uncontrollable cell growth and tumor.
