Tumor(Neoplasm)is a genetic disease,but it is not hereditary;It means that under the effect of tumorigenic factors,the gene of cells has changed,losing the normal regulation of their growth,leading to abnormal proliferation.It can be divided into benign and malignant tumors.The former grows slowly,has a clear boundary with the surrounding tissues,does not transfer,and is not harmful to human health.The latter grows rapidly and can be transferred to other parts of the body.It can also produce harmful substances,destroy the normal organ structure,make the body dysfunctional and threaten life.

Malignant tumors,also known as cancer,are the most serious diseases endangering human health.In the United States,the mortality of malignant tumors is second only to cardiovascular diseases According to the statistical bulletin on the development of health services in China in 2000,the first cause of death of urban residents was malignant tumor,followed by cerebrovascular disease and heart disease.The most common and harmful tumors in China are lung cancer,nasopharyngeal carcinoma,esophageal cancer,gastric cancer,colorectal cancer,liver cancer,breast cancer,cervical cancer,leukemia and lymphoma.

Tumor tissue is composed of parenchyma and stroma.Tumor parenchyma is a tumor cell,which is the main component of tumor and has tissue source specificity.The tumor stroma plays a role in supporting and nourishing the tumor essence.It has no specificity.It is generally composed of connective tissue and blood vessels,and sometimes lymphatic vessels.

Main characteristics of cancer cells

Cancer cells have three significant basic characteristics:immortality,migration and loss of contact inhibition.In addition,cancer cells have many physiological,biochemical and morphological characteristics different from normal cells.

Morphological characteristics of cancer cells

Cancer cells vary in size and shape,usually larger than their source cells.The ratio of nucleus to cytoplasm is significantly higher than that of normal cells,up to 1:1.The ratio of normal differentiated cells is only 1:4-6.

The nuclei vary in morphology,and meganucleus,binuclear or multinuclear phenomena may occur.The chromosomes in the nucleus are aneuploid,with some chromosomes missing and some chromosomes increasing in number.Abnormal changes in normal cell chromosomes will start the process of cell apoptosis,but in cancer cells,signal pathways related to cell apoptosis are blocked,which means that cancer cells are immortal.

Mitochondria show different pleomorphism,swelling and proliferation,such as hypertrophic mitochondria tightly packed in cells in eosinophilic adenoma,and giant mitochondria appear in liver cancer cells.

The cytoskeleton is disordered,some components are reduced,and the cytoskeleton assembly is abnormal.The surface characteristics of cells are changed to produce tumor associated antibody.

Physiological characteristics of cancer cells

The cell cycle is out of control,just like the microorganism parasitic in the cell,which is not controlled by the normal growth control system and can continue to divide and proliferate.

With mobility,the components related to cell adhesion and connection(such as ECM,CAM)are mutated or lost,the relevant signal pathways are blocked,and cells lose the connection between cells and extracellular matrix,which is easy to fall off from tumors.Many cancer cells have the ability of deformation and movement,and can produce enzymes to perforate the vascular basal layer and connective tissue,so that it can migrate to other tissues(Figure 16-1).

Loss of contact inhibition.Normal cells show the characteristics of adherent growth and stop growing after converging into monolayer in vitro culture,that is,contact inhibition,while tumor cells can still grow even if they accumulate in groups(Figure 16-2)

Loss of fixation dependence.Normal eukaryotic cells,except mature blood cells,must adhere to specific extracellular matrix to inhibit apoptosis and survive,which is called anchorage dependency.Tumor cells lose their fixation dependence and can grow on agar,methyl cellulose and other supports.

The phenomenon of dedifferentiation is that more than 20 kinds of fetal isoenzymes are known to be expressed in tumor cells.Fetal alpha fetoprotein(AFP)is specific to the fetus.However,it is expressed in liver cancer cells,so it can be used as a marker for early detection of liver cancer.

The requirement for growth factor is reduced.The requirement for growth factor of cancer cells cultured in vitro is significantly lower than that of normal cells,because the autocrine or the signal pathway of cell proliferation does not depend on growth factors.Some solid tumor cells can also release angiogenesis factors to promote the growth of blood vessels to tumors.Get the nutrients needed for mass reproduction.

The metabolism is vigorous,the DNA and RNA polymerase activities of tumor tissues are higher than those of normal tissues,the nucleic acid decomposition process is significantly reduced,and the content of DNA and RNA is significantly increased.

Both protein synthesis and catabolism are enhanced,but anabolism exceeds catabolism,and can even seize protein catabolites from normal tissues,resulting in the body being in a state of cachexia that is seriously consumed.

Mitochondrial dysfunction,even under the condition of sufficient oxygen supply,is mainly the energy obtained through glycolysis.It is related to the increase in the activity of three key glycolytic enzymes(hexokinase,phosphofructose kinase and pyruvate kinase),the change in the isoenzyme spectrum,and the decrease in the activity of key gluconeogenic enzymes.Transplantability:After normal cells are transplanted into the host,they are rejected due to immune reaction,and most of them are not easy to survive.However,tumor cells are transplantable.For example,human tumor cells can be transplanted into mice to form transplanted tumors.