130
U N I T 1
Cell and Tissue Function
adaptive mechanism for cell replacement when old cells
die or additional cells are needed. Fundamental to the
origin of all neoplasms are the genetic changes that allow
excessive and uncontrolled proliferation that is unregu-
lated by normal growth-regulating stimuli to occur.
Differentiation
is the process of specialization whereby
new cells acquire the structural, microscopic, and func-
tional characteristics of the cells they replace. Neoplasms
are commonly classified as benign or malignant.
Benign
neoplasms
are composed of well-differentiated cells that
resemble the normal counterpart both in terms of struc-
ture and function but have lost the ability to control cell
proliferation.
Malignant neoplasms
are less differentiated
and have lost the ability to control both cell differentia-
tion and proliferation. In general, the better the differen-
tiation of a neoplasm, the slower its rate of growth and
the more completely it retains the functional capabilities
found in its normal counterparts. For example, benign
neoplasms and even well-differentiated cancers of endo-
crine glands frequently elaborate the hormones charac-
teristic of their origin.
Apoptosis
, which is discussed in Chapter 2, is a form
of programmed cell death that eliminates senescent
cells, deoxyribonucleic acid (DNA), and damaged or
unwanted cells. In adult tissues, the size of a population
of cells is determined by the rates of cell proliferation and
death by apoptosis. In malignant neoplasms, the accu-
mulation of neoplastic cells may result not only from
excessive and uncontrolled proliferation, but also from
evasion of apoptosis.
All tumors—benign and malignant—are composed
of two types of tissue: (1)
parenchymal
or specific func-
tional cells of an organ or tissue, and (2) connective
tissue that forms the supporting tissue framework or
stroma.
2.3
The
parenchymal
tissue, which is made up of
the transformed or neoplastic cells of a tumor, deter-
mines its behavior and is the component for which the
tumor is named. The supporting nonneoplastic stromal
tissue component is made up of connective tissue, extra-
cellular matrix, and blood vessels. It is essential to the
growth of the tumor since it carries the blood supply
and provides support for the parenchymal tumor cells.
Terminology
Cancers are commonly referred to as
tumors
or
neo-
plasms
. Although defined in the medical literature as
a swelling that can be caused by a number of condi-
tions, including inflammation and trauma, the term
tumor
is increasingly being used to describe a neoplasm.
Oncology,
from the Greek term
onkos,
for a “swelling,”
refers to the study or science of neoplasms.
Clinical
oncology
deals with neoplastic disorders in the clinical
setting, primarily in terms of diagnosis and treatment.
Benign tumors usually are named by adding the suf-
fix
-oma
to the parenchymal tissue type from which the
growth originated.
2
Thus, a benign epithelial neoplasm of
glandular tissue is called an
adenoma
, and a benign tumor
arising in fibrous tissue is called a
fibroma
. The term
car-
cinoma
is used to designate a malignant tumor of epithe-
lial tissue origin. In the case of malignancies that originate
from glandlike structures, the term
adenocarcinoma
is
used, and for those that originate from squamous cells,
the term
squamous cell carcinoma
is used. Malignant
tumors of mesenchymal origin are called
sarcomas
. A
cancer of fibrous tissue is a
fibrosarcoma
and a malignant
tumor composed of chondrocytes is a
chondrosarcoma.
Papillomas
are benign microscopic or macroscopic
fingerlike projections that grow on any surface. A
polyp
is a growth that projects from a mucosal surface, such as
the intestine. Although the term usually implies a benign
neoplasm, some malignant tumors also appear as pol-
yps. Adenomatous polyps are considered precursors to
adenocarcinomas of the colon. Table 7-1 lists the names
and tissue types of selected benign and malignant tumors.
Biology of Benign and
MalignantTumors
The differences between benign and malignant tumors
are determined by (1) the characteristics of the tumor
cells, (2) the rate of growth, (3) local invasion, and (4)
the ability to metastasize. The characteristics of benign
and malignant neoplasms are summarized in Table 7-2.
Estimated New Cases
Estimated Deaths
Prostate (28%)
Lung and bronchus (14%)
Colon and rectum (9%)
Urinary bladder (6%)
Melanoma of the skin (5%)
Kidney and renal pelvis (5%)
Non-Hodgkin lymphoma (4%)
Leukemia (3%)
Oral cavity and pharynx (3%)
Pancreas (3%)
Breast (29%)
Lung and bronchus (14%)
Colon and rectum (9%)
Uterine corpus (6%)
Thyroid (6%)
Non-Hodgkin lymphoma (4%)
Melanoma of the skin (4%)
Ovary (3%)
Kidney and renal pelvis (3%)
Pancreas (3%)
Lung and bronchus (28%)
Prostate (10%)
Colon and rectum (9%)
Pancreas (6%)
Liver and
intrahepatic bile duct (5%)
Leukemia (4%)
Esophagus (4%)
Urinary bladder (4%)
Non-Hodgkin lymphoma (3%)
Kidney and renal pelvis (3%)
Lung and bronchus (26%)
Breast (14%)
Colon and rectum (9%)
Pancreas (7%)
Ovary (5%)
Leukemia (4%)
Non-Hodgkin lymphoma (3%)
Uterine corpus (3%)
Brain and other
nervous system (2%)
Liver and intrahepatic
bile duct (2%)
*Excludes basal and squamous cell skin cancers and in situ
carcinomas except urinary bladder.
Note: Estimates are rounded to the nearest 10.
FIGURE 7-1.
Ten leading cancer types for the estimated new
cancer cases and deaths in the United States by sex and site,
2013. (Adapted from Siegel R, Naishadham D, Jemel A. Cancer
statistics, 2013. CA Cancer J Clin. 2013;63[1]:11–30.)
