NEOPLASM

Is an abnormal mass of tissue that results when the cells divide more than they should or do not die when they should. (pubmed.com)

A neoplasm (tumor) is a new growth in which cells grow progressively under conditions that do not prompt the growth of normal cells. (www.sciencedirect.com)

A term neoplasm refers to an abnormal growth of tissue caused by the rapid division of cells that have undergone some form of mutation. (www.news-medical.net)

 

CAUSES OF NEOPLASM

There are more than 200 different types of cancer, but all are caused by mutations within the cell’s genetic materials. Some mutations are spontaneous, that is happen by chance during cell division, others are related to exposure to a mutagenic agent (a carcinogen) and a small proportion are inherited. Advancing knowledge in the area has led to identification of many specific genes/ chromosome mutations associated directly with particular cancers.

1.       Carcinogens – These cause malignant changes in cells by irreversibly damaging a cell’s DNA. It is impossible to specify a maximum “safe dose” of a carcinogen. A small dose may initiate change but this may not be enough to cause malignancy unless there are repeated doses over time that have a cumulative effect. In addition, there are widely varying latent periods between exposure and signs of malignancy.

Examples; cigarette smoking which can lead to lung cancer, aniline dyes – predispose to bladder cancer, asbestos – associated with pleural mesothelioma.

2.       Ionizing radiation:  Exposure to ionizing radiation including x-rays, radioactive isotopes, environmental radiation and ultraviolet rays in sunlight may cause malignant changes in some cells and kill others. Examples: repeated episodes of sunburn predispose to development of skin cancer.

3.       Oncogenic Viruses; Some viruses cause malignant changes. Such viruses enter cells and incorporate their DNA or RNA into the host cell’s genetic material, which causes mutation. The mutant cells may be malignant. Examples; Hepatitis B virus causing liver cancer, Human Papilloma Virus causing cervical cancer.

4.       Host factors; Individuals characteristics can influence susceptibility to tumors. Examples; genetic factors, lifestyle factors such as cigarette smoking and etc.

CLASSIFICATION

1.       CLINICAL

The tumor is classified according to its morbid anatomy and behavior. There are two main groups;

·         Benign (simple) tumor

·         Malignant tumor

BENIGN TUMOR

Benign tumors are usually well- encapsulated and well differentiated, retain some normal tissue structure, and do not invade the capsule, nor do they spread to regional lymph nodes or distant locations. Benign tumors are generally named according to the tissues from which they arise with the suffix “oma”

Examples: Leiomyoma (benign tumor of smooth muscle of the uterus), Lipoma (benign tumor of fat cells).

MALIGNANT TUMORS

Are distinguished from benign tumors by more rapid growth rates and specific microscopic alterations, including loss of differentiation; absence of normal tissue organization; lack of capsule; invasion into blood vessels, lymphatics and surrounding structures; and distant spread (metastasis). One of the hallmarks of malignant cells is anaplasia, the loss of differentiation, nuclear irregularities and loss of normal tissue structure.

DIFFERENCES

BENIGN TUMORS	MALIGNANT TUMORS
1.       Remains localized.	1.       Cells transferred via lymphatics, blood vessels, tissue planes and serous cavities to set up satellite tumors (metastases)
2.       Grow slowly	2.       Grow rapidly
3.       Have a well- defined capsule.	3.       Are not encapsulated.
4.       Well- differentiated.	4.       Are poorly differentiated.
5.       Low mitotic index.	5.       High mitotic index.
6.       Are not invasive.	6.       Invades local structures and tissues.

2.       HISTOLOGICAL ORIGIN

Although tumors mat arise from any tissue in the body, they can be conveniently accommodated in five groups;

Ø  Epithelia

Ø  Mesenchymal tissues including fibrous tissue, bone, cartilage and vessels.

Ø  Neuroectoderm

Ø  Haemopoietic and lymphoid cells.

Ø  Germ cells

NOMENCLATURE OF TUMOR

Tumors are named according to the cell type of origin. Cancers arising in epithelial tissue are called carcinomas. Those that arise from ductal or glandular epithelium are named adenocarcinomas. Cancers arising from connective tissue usually have the suffix sarcoma. Example: Rhabdomyosarcomas (cancers of skeletal muscle)

Cancers of lymphatic tissue are lymphomas. Cancers of blood- forming cells are named as leukemias.

GENERAL HISTOLOGY OF BENIGN TUMORS

1.       They mimic the structure of their parent organ.

2.       Resemble the cells of their tissue of origin.

3.       As in normal tissue, they show a remarkable uniformity is size, shape and nuclear configuration.

4.       They show evidence of normal function.

5.       They have relatively infrequent mitotic figures.

 GENERAL HISTOLOGY OF MALIGNANT TUMORS

1.       They generally show a haphazard arrangement. Example; Carcinoma of breast.

2.       They bear little resemblance to the cells of origin.

3.       They tend to vary widely in size, shape and nuclear configuration, reflecting an increase in chromosomal number and DNA content (Aneuploidy) Example; Pleomorphic sarcoma.

4.       They provide little evidence of normal function. Example: Adeno carcinoma of bowel.

5.       They show frequent mitoses often of abnormal type.

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