GENERAL INFORMATION ON TUMORS
A/ Definition
A tumor is “a new tissue formation (more or less voluminous) resembling (more or less) the homologous normal tissue (adult or embryonic) at the expense of which it has developed, which tends to persist and increase and which escapes the biological rules of growth and cellular differentiation”. Currently, the term “tumor” tends to be used in the sense of neoplasm or “neoplasia”.
Formerly, but also currently in the Anglo-Saxon literature, the term “tumor” was used to refer to any localized increase in volume of an organ or region of the body. This increase could correspond to pathological processes of different nature: true tumor, pseudo tumor (inflammatory and dystrophic), dysembryoplasia (hamartomas and choristomas), hyperplasia and hypertrophy. This definition now corresponds to that of the term “tumefaction”.
TUMORS THEREFORE PRESENT THE FOLLOWING CHARACTERS
Qualitatively and quantitatively abnormal proliferation of the cellular elements of an organized tissue.
Excessive and uncoordinated growth of the tumor relative to neighboring tissues.
Tumor autonomy. Tumor proliferation continues after the “stimulus” that gave rise to it has stopped.
Biological independence from the organism. It escapes any control.
1. Pseudo tumors
Some lesions can be confused with neoplasms. They must be distinguished from true tumors.
a) Inflammatory pseudotumors
Inflammatory pseudotumors are local increases in the volume of a tissue or organ, due to an inflammatory reaction that is generally subacute or chronic. There could be many examples:
Hyperplastic fleshy bud: cutaneous botryomycoma, gingival epulis
Foreign body reaction.
Hypertrophic scar (keloid).
b) Dystrophic pseudotumors
The term dystrophic lesion means “lesion secondary to a nutritional, endocrine, vascular disorder affecting cellular trophicity”. In relation to stimuli
c) Malformative pseudotumors
These are lesions secondary to a disorder of organogenesis.
d) Choristoma ( Greek choristos: separated; -oma: tumor) can be defined as the presence of cells or tissue of normal microscopic appearance and normally absent in the location considered (heterotopia).
e) Hamartoma (Greek hamartenian: to miss the mark; -oma; tumor) is defined as the presence of cells or tissue of normal microscopic appearance and normally present for the organ considered but in excessive quantity or abnormal arrangement (it is therefore not a heterotopia). The cellular elements are mature and identical to the cellular elements of the organ where it is located but the architectural organization is different from that of the tissues surrounding the lesion. The demarcation between hamartoma and benign tumor is tenuous.
Examples:
Lymphangiomas and hemangiomas are sometimes hamartomas
f) Embryonic remnants (vestigial heterotopias) This is the persistence of an embryonic structure which should have disappeared.
2. Classification of tumors
a) Certain criteria classically distinguish “benign” tumors from “malignant” tumors
1. Clonality
A clone is derived from a single initial cell.
A tumor developing from a group of cells is said to be polyclonal.
A tumor developing from a few cells is said to be oligoclonal.
A tumor developing from a single cell is said to be monoclonal.
Malignant tumors are monoclonal (tumor proliferation corresponds to the same cell clone). Although some benign tumors may be monoclonal, monoclonality remains, most often, a criterion of malignancy, particularly in lymphoid tumors. To demonstrate the clonality of a B or T lymphoid population, the rearrangement of the immunoglobulin heavy chain gene or the T receptor gene is studied by Southern blot or by PCR amplification. For other tumors, the monoclonal nature of a cell population can be demonstrated by different molecular biology techniques (study of the X chromosome inactivation profile in women).
2. Differentiation
Differentiation reflects the degree of resemblance, morphological and functional, between neoplastic cells and the normal cells that originally gave rise to them .
Well-differentiated tumors are made up of cells that resemble the cells of the tissue that gave rise to them. Poorly differentiated or undifferentiated tumors are made up of young cells.
As a rule, all benign tumors are well differentiated. In a benign smooth muscle cell tumor – or leiomyoma – the tumor cells are similar to normal smooth muscle cells, only the nodular organization of these cells reflects their tumoral nature.
Malignant tumors can be well differentiated, poorly differentiated, or undifferentiated.
Completely undifferentiated malignant tumors are called anaplastic. The absence of differentiation is a formal characteristic of malignancy. Thus, in all specialized epithelial tissues, a malignant tumor develops from reserve cells or stem cells. In well-differentiated malignant tumors, differentiation occurs by maturation. In undifferentiated malignant tumors , the malignant neoplastic cells do not undergo maturation. In fact, the absence of differentiation does not mean dedifferentiation.
GENERAL INFORMATION ON TUMORS
3. Growth rate
Most benign tumors grow slowly over a period of years, while most malignant tumors grow rapidly. However, these statements must be qualified. Some benign tumors grow rapidly, but their growth can be disrupted by many factors, such as insufficient blood supply. The growth rate is most often correlated with the degree of differentiation, so malignant tumors have a higher growth rate than benign tumors. However, malignant tumors can behave differently. Some of them grow very rapidly and can metastasize and kill the carrier within a few months. Others have a slower development, or even phases of remission.
4. Local invasion
Benign tumors remain localized to the tissue that gave rise to them, they do not spread to a distance and do not give rise to metastases. The slow growth of the tumor will allow the displacement of neighboring tissues. The compressed connective tissue forms a capsule surrounding the tumor. Malignant tumors develop by destroying the neighboring tissue. They are, most often, poorly limited and not encapsulated. Tumor invasion is one of the most reliable criteria for diagnosing malignant tumors.
5. Metastases
Metastases unequivocally determine the malignant nature of a tumor because benign tumors never metastasize.
CRITERIA FOR DISTINGUISHING BENIGN AND MALIGNANT TUMORS
Benign tumors Malignant tumors
Macroscopy
Well limited. Badly limited.
Encapsulated. Not encapsulated.
Microscopy
Similar to the original fabric. More or less similar to the original fabric.
No cytological criteria of malignancy Cytological criteria of malignancy
Slow growth Fast growth
Repression without destruction of neighboring tissues Invasion of neighboring tissues
Evolution
No recurrence after complete excision Recurrence possible after supposedly total excision
NO METASTASIS M ETASTASIS
Nomenclature of tumors
Fabric from Benin Malin
Epithelial tissue
Stratified malpighian Squamous papilloma Squamous cell carcinoma
Glandular epithelium Adenoma Adenocarcinoma
Common connective tissue
Fibroblasts Fibroma Fibrosarcoma
Specialized connective tissue
Adipose tissue Lipoma Liposarcoma
Smooth muscle tissue Leiomyoma Leiomyosarcoma
Striated muscle tissue Rhabdomyoma Rhabdomyosarcoma
Vascular Angioma Angiosarcoma
Cartilaginous Tissue Chondroma Chondrosarcoma
Bone tissue Osteoma Osteosarcoma
Hematopoietic tissue
Lymphoid Lymphomas and Hodgkin’s Disease
Nervous tissue
Meninges Meningioma Malignant meningioma
Peripheral nerve Schwannoma. Neurofibroma Malignant Schwannoma
Melanin tissue
Nevocellular nevus Melanoma
GENERAL INFORMATION ON TUMORS
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