Neoplasia 1

Neoplasia

Neoplasia Definition

• New growth.

• Abnormal mass of tissue with excessive and uncoordinated growth that persists even after the removal of stimuli.

• A disorder of cell growth triggered by acquired mutations in a single cell and its progeny.

Key Points

• Cell proliferation: Increase in cell number due to growth and division.

• Cell growth: Increase in cell volume without an increase in cell number.

• Cell division: Formation of two daughter cells from a parent cell.

• Cell differentiation: Acquisition of specialized function and morphology by a less specialized cell.

• Differentiation often involves stages and is associated with permanent exit from the cell cycle.

• Fully differentiated cells cannot divide further.

• Inverse relationship between proliferation and differentiation during normal development.

Classification

• Based on a judgment of a tumor’s potential clinical behavior.

• Benign neoplasia: Proliferate and divide but do not invade surrounding tissues or metastasize.

• Malignant neoplasia (Cancer): Invade and/or metastasize. Progressive clinical course; may result in death without adequate therapy.

Characteristics of Benign Neoplasia

• Relatively innocent gross and microscopic morphology.

• Remain localized without invasion or metastasis.

• Well-differentiated: Cells closely resemble tissue of origin.

• Good prognosis; often curable by surgical removal.

• Grow slowly and are clearly demarcated.

• Nuclear morphology often normal.

• Low mitotic rate with normal features.

• Clonal chromosome abnormalities, but typically not aneuploid.

Characteristics of Malignant Neoplasia

• Invasion: Infiltrate adjacent tissues or structures.

• Metastasis: Spread to distant sites.

• Differentiation range: Well-Moderated-Poorly-Undifferentiated-Dedifferentiated.

• Variable prognosis.

• Rapid growth and not clearly demarcated.

• High mitotic rate with abnormal features.

• Usually aneuploid.

Six P's of Malignant Neoplasm

• Purposeless

• Progressive

• Proliferation unregulated

• Preys on host

• Persists even after withdrawal of stimulus (autonomous)

• Permanent genetic change in the cell

Fundamental Features of Benign and Malignant Neoplasms

• Differentiation and anaplasia.

• Differentiation: Extent to which neoplasms resemble their parenchymal cells of origin.

• Anaplasia: Lack of differentiation.

• Local invasion.

• Metastasis.

Differentiation

• Benign: Well-differentiated cells resembling normal counterparts.

• Malignant: Wide range of differentiation; may exhibit morphologic alterations.

• Well-differentiated cancers: Resemble normal cells but invade.

• Poorly differentiated: Little resemblance to cell of origin.

• Moderately differentiated: Intermediate differentiation.

Anaplastic Tumors

• Anaplasia: Reversal of differentiation to a more primitive level.

• The degree of anaplasia in a cancer cell correlates with the aggressiveness of the tumor.

Local Invasion

• Benign tumors grow as cohesive, expansile masses that remain localized.

• Malignant tumors are characterized by progressive infiltration, invasion, and destruction of surrounding tissues.

Metastasis

• Definition: Tumor deposits discontinuous with the primary tumor and located in a distant tissue.

• Metastasis identifies a tumor as malignant; benign tumors do not metastasize.

• Invasiveness allows cancer to penetrate vessels and cavities, facilitating spread.

• Metastasis reduces the possibility of cure and is a common cause of cancer death.

Components of Neoplasms

• Parenchyma: Neoplastic cells.

• Stroma: Supporting, non-neoplastic tissue from the host, including connective tissue, blood vessels, and inflammatory cells, required for tumor growth and survival.

Nomenclature of Neoplasms

• Tumor names usually refer to cellular origin and behavior.

• Four tissue types: Epithelial, Nervous, Muscle, Connective.

• Epithelial tumors.

• Mesenchymal tumors.

Naming Conventions

• Benign Tumors: Named with the suffix “oma” attached to the cell of origin (e.g., Lipoma).

• Malignant Tumors: Termed carcinoma or sarcoma depending on the parenchymal cell of origin (e.g., Liposarcoma, Adenocarcinoma).

Confusing Terminology

• Polyp: Neoplasm that produces a visible projection above a mucosal surface.

• Hamartoma: Mass of disorganized tissue indigenous to a particular site.

• Choristoma: Ectopic island of normal tissue in an abnormal site.

• Melanoma: Malignant neoplasia of melanocytes.

• Lymphoma: Malignant neoplasia of lymphoid tissue.

• Seminoma: Malignant testicular neoplasia.