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VetBooks.ir Chapter 20

Carcinogenesis: Mechanisms and Models *

Supratim Choudhuri, Ronald Chanderbhan and Antonia Mattia

INTRODUCTION carcinoma), squamous cell carcinoma, small cell carci-
noma, large cell carcinoma, etc. The most common
Cancer is a general term used to refer to a pathological
types of cancers in humans are carcinomas. Cancers of
condition that is characterized by aberrant cell growth and
embryonic tissues are denoted with the suffix “blasto-
proliferation. Carcinogenesis is the process of cancer
ma,” such as neuroblastoma and retinoblastoma.
development. Animals, like humans, have always been
Similarly, cancers of connective tissue, such as bone,
exposed to thousands of man-made and naturally occur-
cartilage, fat, muscle, and blood vessels are denoted
ring chemical substances in their daily lives. This expo-
with the suffix “sarcoma,” such as fibrosarcoma, lipo-
sure may come from the food they eat, the water they
sarcoma, and rhabdomyosarcoma.
drink, and the air they breathe. Both the level of exposure
Sometimes nonneoplastic lesions end with the “oma”
and duration of exposure are factors that impact whether
suffix, such as hematoma and granuloma. A hematoma is
chemicals cause cancer in humans and animals. In 1915,
a localized collection of blood outside the blood vessels
Katsusaburo Yamagiwa and Koichi Ichikawa at Tokyo
that occurs when blood escapes into the surrounding tis-
University pioneered the field of experimental cancer
sue because of damage to the blood vessels. A granuloma
research when they produced tumors by repeated applica-
is a small patch of inflamed tissue that results from
tion of coal tars on the skin of rabbits. Over the last
infection or inflammation. The terms used to describe
50 years or so, remarkable progress has been made in
these noncancer tissue alterations are a reminder that the
understanding the mechanism of carcinogenesis, which
terminology surrounding cancer and carcinogenesis is not
has both a genetic and an environmental component. The
simple. Tumor typing and cancer diagnosis require the
present chapter primarily focuses on the mechanism and
expertise of trained pathologists.
models of chemical carcinogenesis.
TERMINOLOGY AGENTS CAUSING CARCINOGENESIS
Three main types of agents that can lead to the develop-
Tumors or neoplasms (new growth of tissue) can be
ment of cancer are chemicals, viruses and radiation.
benign or malignant (cancerous). In the parlance of can-
Chemical carcinogenesis is an important topic in toxicol-
cer biology, the suffix “oma” means tumor—whether
ogy and will be the primary focus of this chapter. The
benign or malignant. For example, adenoma, fibroma,
genetic basis of carcinogenesis including virus-induced
and lipoma are benign tumors of glandular, fibrous
carcinogenesis and radiation-induced carcinogenesis will
(connective), and adipose tissues, respectively, while
be discussed briefly.
melanoma, hepatoma, and seminoma are malignant
tumors of skin, liver, and germ cells, respectively.
Cancer arising in the epithelial tissues lining the outer
or inner surfaces of the body is called carcinoma. Chemical Carcinogenesis
Carcinomas are classified according to histological Chemical Carcinogens Occur in Nature
type, and include adenocarcinoma (glandular
and Can Also Be Formed by Nonindustrial
and Industrial Processes
* The opinions expressed in this chapter are the authors’ personal opin-
ion and they do not necessarily reflect those of FDA, DHHS, or the fed- Chemical carcinogens are extremely diverse in structure
eral government. and they belong to very different chemical classes,
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00020-9
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