Neoplasia

NEOPLASIA

DEFINITION
A neoplasm is an abnormal mass of tissue, the growth of which is virtually autonomous and exceeds that of normal tissues. Unlike non-neoplastic proliferations (like hyperplasia, regeneration and repair), the growth of neoplasms persist after the cessation of the stimuli that have initiated the change.
Neoplasms (tumors) are generally classified into two broad categories, benign and malignant.

NOMENCLATURE:

All neoplasms have two basic components
The transformed neoplastic cells (the parenchyma)
The supportive stroma.
The latter is composed of non-transformed (non-neoplastic) elements, such as connective tissues and blood vessels.

Classifications of neoplasms are based on their parenchymal components.

BENIGN TUMORS
In general their names end with the suffix oma.

Benign mesenchymal tumors are named after their tissue of origin + oma

Examples
Leiomyoma  HYPERLINK "photo%20neoplasia/Leiomyomas%20uteri.ppt"
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Lipoma
Chondroma,
Schwannoma, etc.


Benign epithelial tumors are named after their tissue of origin, sometimes combined with architecture + oma.
Examples
Adenomas are tumors arising from glandular tissue and usually form glandular patterns
Cystadenomas as above but with cystic components
Papillary cystadenoma as above but with papillary (warty or finger-like projections)  HYPERLINK "photo%20neoplasia/Ovarian%20cystadenoma%20and%20papillary%20cystadenoma.ppt"
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Papillomas characterized by the production of finger like projections.  HYPERLINK "photo%20neoplasia/Squamous%20papilloma%20larynx.ppt"
[]  HYPERLINK "photo%20neoplasia/Papilloma%20colon.ppt"
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MALIGNAT TUMORS

These are generally called cancers.
Their nomenclature is based on their appearance (the morphology of their parenchymal cells) and the presumed tissue of origin.

Theyre broadly divided into two categories

Carcinomas arising from epithelial cells
Examples include
Squamous cell carcinomas,
Adenocarcinoma,
small cell undifferentiated carcinomas, etc.

Sarcomas arising from or differentiating towards mesenchymal tissues

Examples include
Osteosarcomas
Leiomyosarcomas,
Rhabdomyosarcomas.


Some tumors have more than one parechymal cell type, these include
1. Teratomas, which are tumors of germ cell origin, showing differentiation along all the three germ layers (Ectoderm: like skin and its adnexae such as hair follicles and sebaceous glands, Endoderm: like gut epithelia and Mesoderm: like bone, cartilage, muscle, etc), thus a variety of parenchymal cell types may be seen in any one of these neoplasms.
Examples include
teratoma of the ovary
teratoma of the testis



Mixed tumors; these differ from teratomas in that they are derived from one germ cell layer, that differentiates into more than one parenchymal cell type.
Examples include
Pleomorphic adenoma of salivary glands
Fibroadenoma of breast

EXCEPTIONS

Exceptions to the above mentioned rules include tumors that are always malignant such as
Lymphomas (tumors of lymphoid tissue).
melanomas (malignant tumors of melanocytes)
Seminomas and Dysgerminomas (tumors of primitive germ cells) .

CHARACTERISTICS OF BENIGN AND MALIGNANT TUMORS

BENIGN TUMORSMALIGNANT TUMORSMode of growthExpansion,
Remain localizedInfiltrates locally and
Metastasizes.Rate of growthSlowerFasterHistological features
Similar to tissue of origin.

Nuclei are normal.

Cells uniform in size and shape.Many differ from tissue of origin.

Enlarged pleomorphic

nuclei, hyerchromasia,
Prominent nucleoli,
Increased mitotic activity,
abnormal mitosis.

Cellular pleomorphism in

size and shape.Clinical effectsLocal pressure effects.

Hormone secretion.

Cured by adequate excision.Local pressure and tissue destructive effects.


Inappropriate hormone secretion.

Not cured by local excision because of metastasis.

Paraneoplastic syndromes.

DIFFERENTIATION AND ANAPLASIA

Differentiation is the extent to which tumor cells resemble comparable normal cells of the tissue of origin.
In most benign tumors the constituent cells closely mimic corresponding normal cells.
Malignant tumors display a range of differentiations that form the basis of tumor grading.
Lack of differentiation (anaplasia) is the hallmark of malignant cells.

Histopathological features of anaplasia:

Cellular and nuclear pleomorphism refers to variation in size and shape of cells and their nuclei.

Hyperchromatism refers to dark staining of nuclei due to abnormally increased chromatin (nucleic acids contents), a reflection of aneuploidy.

Increased nuclear-cytoplasmic ratio (N/C) reaching nearly 1:1 (instead of the normal 1:4-6).

Abundant mitoses reflecting increased proliferative activity

Abnormal mitoses, e.g., tripolar spindles (normally mitosis is bipolar).

Tumor giant cells containing a single giant polypoid nucleus or multiple nuclei.

Prominent nucleoli

Cytoplasmic basophilia reflecting active protein synthesis.

Loss of orientation and disarray of tissue architecture (loss of polarity).


RATE OF GROWTH
Most cancers grow faster than benign tumors.

Some cancers grow slowly for years then enter a phase of rapid growth; others are rapid from the outset.

Some cancers are hormone sensitive and may be affected by variation in hormone levels associated with pregnancy and menopause (e.g., breast cancer). Other hormone sensitive cancers include endometrial adenocarcinoma (estrogen dependent) and prostatic adenocarcinoma (androgens dependent).

Rapidly growing tumors may develop central areas of ischaemic necrosis because they outgrow their blood supply.

LOCAL INVASION

Most benign tumors grow as cohesive expansile masses that develop a rim of condensed connective tissue or capsule at the periphery . They dont penetrate the capsule or the surrounding normal tissues. The line of cleavage between the capsule and the surrounding normal tissues facilitates surgical enucleation.
Malignant tumors are invasive (infiltrative), they invade and destroy normal surrounding tissues. They usually lack a well-defined capsule or line of cleavage, thus, their enucleation is impossible, and their surgical removal requires removal of a considerable margin of healthy apparently uninvolved tissue.





METASTASIS


This process involves invasion of blood vessels, lymphatics and body cavities by the malignant tumor, followed by the transport and growth of secondary tumor cell masses that are discontinuous with the primary tumor. These are called secondaries.

Metastasis is the absolute criterion of malignancy.

Except basal cell carcinomas of the skin and brain tumors, almost all malignant tumors have the capacity to metastasize.

Routes of tumor spread and metastasis

Local spread this occurs by invasion into the adjacent tissues.

Invasion of lymphatics (lymphatic spread). This is followed by spread of the tumor to regional lymph nodes and ultimately to other sites in the body. It is common in the initial spread of carcinomas. Not all enlarged lymph nodes located at the sites of drainage of a malignancy means necessarily a metastasis. This is because immune responses to tumor antigens can result in nodal enlargement too. The latter is through the development of lymphoid hyperplasia.


Invasion of blood vessels (hematogenous spread). This is typical of all sarcomas, but is also the favored route for certain carcinomas (e.g., renal cell carcinoma). Because of their thinner walls, veins are more readily and thus more frequently invaded than arteries. Lungs and liver are the commonest site of hematogenous spread because they receive the systemic and portal venous blood respectively. Other major sites are the bones and brain.

Spread into body cavities (transcelomic spread). This occurs by seedlings of surfaces of peritoneal, pleural, pericardial and subarachnoid spaces. Carcinoma of the ovary spreads transperitoneally to the surface of the liver or other abdominal viscera (transcelomic spread).