Growth of Tumors
When an overgrowth of tissue forms into neoplastic mass, it’s called a neoplasm or tumor. Neoplasia can have a deadly outcome such as in cancer. It is the No. 2 killer in North America with 30 percent suffering from the disease. A quarter of North American adults die of cancer. It also kills more children than any other disease.
Oncology is the study of tumors and when we talk about tumors, there’s two important characteristics – pattern of growth and tissue of origin. A tumor is benign if growth is slow, orderly and the tumor is localized. It’s malignant if the growth is rapid, disorderly and invades other normal tissues. Cancer is result of a malignant tumor that spreads to distant points in the body.
We add the suffix “-oma” when designating a benign tumor and what in which tissue it originates. An osteoma is a benign tumor in bone. A fibroma is a benign tumor in fibrous tissue.
If a malignant tumor arises, then it is named depending on which embryonic tissue it originates from. If from the ectoderm or dndoderm, then it’s a carcinoma (usually skin and epithelial linings). If it’s a glandular tumor, then it’s called an adenocarcinoma. If it occurs in the mesoderm, then it’s a sarcoma such as a chondrosarcoma or fibrosarcoma.
Then, there are exceptions, such as melanoma, lymphoma, and hepatoma which sound benign but are actually malignant. Malignant tumors in leukocyte-producing tissues are myeloid leukemia (red bone marrow) and lymphcytic leukemia (lymphoid tissue).
A benign tumor’s cells are about normal size and shape and pretty much looks like normal tissue, but a malignant tumor is very pleomorphic, enlarged and contains abnormal nuclei and chromosome structures. Sometimes the cells are huge because they fail to undergo mitosis.
Benign tumors grow faster than normal, but are slower than malignant tumors. They also have a fibrous connective tissue capsule surrounding the mass, which creates a distinct line to separate it from normal tissue. Generally, the slow growth causes less damage and surgical removal leads to a pretty good prognosis.
Malignant tumors grow quickly and are aggressive in their invasion. They send whole columns of cells to disrupt other normal tissues. They rarely come within a capsule as the benign tumors do. The line is blurred between malignant tumor tissue and normal tissue. Metastasis is a major factor causing a poor prognosis as growth at primary sites usually lead to establishment of tumors in secondary sites.
A spread of malignant tumor to secondary sites increases damaging effects. The metastasis of tumor cells often are carried by blood or lymph. If the invasion of a vein or lymphatic vessel occurs, then an emboli is formed that is used to gain access to a secondary site. Capillaries and lymphatic vessels are easily invaded, especially by carcinomas.
Metastasis can also involve spreading through body cavities. These can include adenocarcinomas shedding from the pancreas into the pelvic cavity or when a neuroblastoma from a the medulla oblongata spreads to the subarachnoid space invading the spinal canal.
Iatrogenic metastasis is rare. It occurs when medical intervention introduces tumor tissue to a site to develop into a secondary tumor.
Tumors growth at primary and secondary sites impairs normal functions. Malignant tumors cause continual increased damage, which generally overwhelm the body despite therapy.
Nowak TJ, Hanfod AG. Pathophysiology: Concepts and applications for health care professionals, 3rd ed. 2004. New York, McGraw-Hill.