636
U N I T 7
Kidney and Urinary Tract Function
MalignantTumors of the Kidney
There are two major groups of malignant tumors of the
kidney: embryonic kidney tumors (i.e., Wilms tumor),
which occur during childhood, and renal cell carcinoma,
which occurs in adults.
WilmsTumor
Wilms tumor, also known as
nephroblastoma,
is one
of the most common primary neoplasms of young chil-
dren. It usually presents between 3 and 5 years of age
and is the second most common malignant abdominal
tumor in children.
4,32
It may occur in one or both kid-
neys. The incidence of bilateral Wilms tumor is 6% to
7%, with children having a horseshoe kidney being at
twice the risk.
Histologically, the tumor is composed of elements
that resemble normal fetal tissue: blastemic, stromal,
and epithelial. An important feature of Wilms tumor
is its association with other congenital anomalies,
including aniridia (absence of the iris), hemihypertro-
phy (enlargement of one side of the face or body), and
other congenital anomalies, usually of the genitouri-
nary system. Several chromosomal abnormalities have
been associated with Wilms tumor. One Wilms tumor
gene,
WT1
located on chromosome 11, is a tumor-suppressor gene that regulates several other growth
factor genes.
32
Wilms tumor usually is a solitary mass that occurs in
any part of the kidney. It usually is sharply demarcated,
variably encapsulated, and grows to a large size, dis-
torting kidney structure (Fig. 25-16). The tumors usu-
ally are staged using the National Wilms Tumor Study
Group classification.
32
Stage I tumors are limited to the
kidney and can be excised with the capsular surface
intact. Stage II tumors extend into the renal capsule but
can be excised. In stage III, extension of the tumor is
confined to the abdomen, and in stage IV, hematogenous
metastasis most commonly involves the lung.
The common presenting signs are a large asymp-
tomatic abdominal mass and hypertension. The tumor
is often discovered inadvertently, and it is not uncom-
mon for the parent to discover it while bathing the child.
Some children may present with abdominal pain, vomit-
ing, or both. Microscopic and gross hematuria is pres-
ent in 15% to 25% of children. CT scans are used to
confirm the diagnosis.
32
Treatment involves surgery, chemotherapy, and
sometimes radiation therapy. Long-term survival rates
have increased to more than 70% for all stages and to
91% to 96% for stages I through III.
32
Renal Cell Carcinoma
Cancer of the kidney is the seventh leading malignancy
among men and the twelfth among women, account-
ing for about 3% of all cancers.
33
Incidence peaks
between 55 and 84 years of age.
34
Renal cell carcinoma
accounts for approximately 80% to 90% of all kidney
cancers.
4,5,33–35
Most renal cell carcinomas are sporadic,
but about 5% are inherited. Inherited tumors tend to
be multifocal and bilateral, and appear at an earlier age
than sporadic renal cell carcinomas.
A major advance in the understanding of renal cell
carcinoma has been the realization that this neoplasm is
not a single entity, but a collection of tumors that arise in
different parts of the tubular or ductal epithelium. Clear
cell carcinomas, so named because of their high cyto-
plasmic lipid content, accounts for 70% to 80% of all
renal cell carcinomas.
5
They arise from proximal tubular
epithelial cells and appear as solitary unilateral lesions
located predominantly in the renal cortex (Fig. 25-17).
Papillary carcinomas, which are characterized by a pap-
illary growth pattern, account for another 10% to 15%
of renal cancers.
5
Thought to arise from the proximal
tubules, they can be multifocal and bilateral.
The cause of renal cell carcinoma remains elusive.
Epidemiologic evidence suggests a correlation between
heavy smoking and kidney cancer.
33,34
Obesity also is a
risk factor, particularly in women. Additional risk fac-
tors include occupational exposure to petroleum prod-
ucts, heavy metals, and asbestos.
5
The risk for renal cell
carcinoma also is increased in persons with acquired
cystic kidney disease associated with chronic renal
insufficiency.
Kidney cancer is largely a silent disorder during its
early stages, and symptoms usually denote advanced
FIGURE 25-16.
Wilms tumor. A cross-section of a pale tan
neoplasm (arrow) attached to a residual portion of the kidney.
(From Jennette JC.The kidney. In: Rubin R, Strayer DS, eds.
Rubin’s Pathology: Clinicopathologic Foundations of Medicine.
6th ed. Philadelphia, PA: Wolters Kluwer Health | Lippincott
Williams &Wilkins; 2012:805.)
