HUMAN BIOLOGY

436 Chapter 22

expLoreon your own

summary

section 22.1 Overgrowing cells lead to
a tissue mass called a tumor. In dysplasia, a
common precursor to cancer, cells develop
abnormalities in size, shape, and organization.
Cancer results when the genetic controls over
cell division are lost completely. Cancer cells
(Figure 22.18) differ from normal cells in both structure and
function. They usually have an overly large nucleus and altered
surface proteins, and lack features of a normal, specialized
body cell. Cancer cells also grow uncontrolled and can invade
surround ing tissues, a process called metastasis.

sections 22.2, 22.3 Cancer develops
during carcinogenesis, a process that
involves a series of genetic changes. Initially,
mutation may alter a proto-oncogene into
a cancer-causing oncogene. Infection by a
virus can also insert an oncogene into a
cell’s DNA or disrupt normal controls over
a proto-oncogene. One or more tumor suppressor genes must
be missing or become mutated before a normal cell can be
transformed into a cancerous one (Table 22.5).
A predisposition to a certain type of cancer can be inherited.
Other causes of carcinogenesis are viral infection, chemical
carcinogens, radiation, faulty immune system functioning, and
possibly a breakdown in DNA repair.

section 22.4 In general, a cancer is named

according to the type of tissue in which it arises.

Common ones include sarcomas (connective

tissues such as muscle and bone), carcinomas

(epithelium), adenocarcinomas (glands or their

ducts), lymphomas (lymphoid tissues), and

leukemias (blood-forming regions).

section 22.5 Common methods for

cancer diagnosis include blood testing for

the presence of substances produced either

by specific types of cancer cells or by normal

cells in response to the cancer. Medical

imaging (such as magnetic resonance

imaging) also can aid diagnosis. Biopsy

provides a definitive diagnosis.

section 22.6 Cancer treatments

include surgery, chemotherapy, and tumor

irradiation. Under development are target-

specific monoclonal antibodies and immune

therapy using interferons.

Lifestyle choices such as the decision not

to use tobacco, to maintain a low-fat diet,

and to avoid overexposure to direct sunlight and chemical

carcinogens can help limit personal cancer risk.

Figure 22.18 This cancer cell is surrounded by white blood

cells that may or may not be able to destroy it. The cancer

cell has extended dozens of “false feet” (pseudopodia) that

help it move about in tissues.

Lennart Nilsson © Boehringer Ingelheim International GmbH

Most families have been touched by cancer in one way or another. The American Cancer

Society website is a portal to a huge amount of reliable information on the risks for, causes of, and

treatments for virtually any cancer. Choose a cancer to investigate and see how much you can learn

about it in just 15 minutes. Does your research give you any new insights into your own risk for the

cancer? What is your reaction to the stories of cancer survivors that are posted on the website?

Dr. Pascal Madaule, Paris

Dividing cervical cancer cells

Table 22.5 Cancer Causes and Contributing Factors

Cause/Factor Impact

Oncogene May alter control of cell division

Faulty tumor Fails to halt runaway cell division

suppressor gene

Viral infection Switches proto-oncogene to oncogene or

inserts an oncogene into the host cell DNA

Carcinogen Damages DNA

Radiation Damages DNA

Faulty immunity Fails to tag cancer cells for destruction

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