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Respiratory Tract Infections, Neoplasms, and Childhood Disorders
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carcinoma tends to originate in the central bronchi as an
intraluminal growth and is thus more amenable to early
detection through cytologic examination of the sputum
than other forms of lung cancer.
13
It tends to spread cen-
trally into major bronchi and adjacent intrapulmonary
lymph nodes (Fig 22-9). Central cavitation of the tumor
is frequent.
Currently,
adenocarcinoma
is the most common sub-
type of lung cancer in North America.
13,14
Its association
with cigarette smoking is weaker than for squamous cell
carcinoma. It is the most common type of lung cancer
in women and nonsmokers. Adenocarcinoma is a malig-
nant epithelial cell tumor with glandular differentiation
or mucin production by the tumor cells. These tumors
tend to be located more peripherally than squamous cell
sarcomas and are often associated with pleural fibrosis
and scarring (Fig. 22-10). In general, adenocarcinomas
have a poorer stage-for-stage prognosis than squamous
cell carcinomas.
Large cell carcinomas
have large, polygonal cells.
They constitute a group of neoplasms that are highly
anaplastic and difficult to categorize as squamous cell
carcinoma or adenocarcinoma. They tend to occur in
the periphery of the lung, invading subsegmental bron-
chi and larger airways. They have a poor prognosis
because of their tendency to spread to distant sites early
in their course.
13,14
Small Cell Lung Cancer
Small cell lung cancer is characterized by a distinctive
cell type—small round to oval cells that are approxi-
mately the size of a lymphocyte.
13,14,49,50
The cells grow
in clusters that exhibit neither glandular nor squamous
organization. The tumors are thought to arise from the
neuroendocrine cells of the bronchial epithelium, and
some of the tumor cells may be able to secrete hormon-
ally active products. This cell type is associated with
several types of paraneoplastic syndrome (signs and
symptoms caused by secretions of or immune response
to tumor cells), including the syndrome of inappropriate
antidiuretic hormone secretion (SIADH; see Chapter 8).
This type of cancer has the strongest association with
cigarette smoking and is rarely observed in someone
who has not smoked.
Small cell lung cancer is highly malignant, tends to
infiltrate widely, disseminate early, and is rarely resect-
able. About 70% of the cancers have detectable metasta-
ses at the time of diagnosis; the rest are assumed to have
micrometastases. Brain metastases are particularly com-
mon with SCLC and may provide the first evidence of
the tumor. Response rates for treatment with chemother-
apy (cisplatin and etoposide) are excellent, with 50% to
60% complete response in persons with limited disease
and 15% to 20% complete response in those with exten-
sive disease.
47
However, remissions tend to be short-lived
with a mean duration of 6 to 8 months. Once the disease
has recurred, the mean survival length is 3 to 4 months.
Overall the 2-year survival is 20% to 40% in limited-
stage disease and less than 5% in extensive disease.
Clinical Features
Lung cancers are aggressive, locally invasive, and widely
metastasizing tumors. Squamous cell and adenocarcino-
mas usually begin as small mucosal lesions that may fol-
low one of several patterns of growth. They may form
intraluminal masses that invade the bronchial mucosa
and infiltrate the peribronchial connective tissue, or
they may form large, bulky masses that extend into
the adjacent lung tissue. Some large tumors undergo
FIGURE 22-9.
Squamous cell carcinoma of the lung in which
the tumor grows within the lumen of a bronchus and invades
the adjacent intrapulmonary lymph node. (From Beasley MB,
TravisWD, Rubin E.The respiratory system. In: Rubin R, Strayer
DS, eds. Rubin’s Pathology: Clinicopathologic Foundations of
Medicine. 6th ed. Philadelphia, PA: Wolters Kluwer Health |
Lippincott Williams &Wilkins; 2012:595.)
FIGURE 22-10.
Adenocarcinoma of the lung. A peripheral
tumor is located in the upper right lobe of the lung. (From
Beasley MB,TravisWD, Rubin E.The respiratory system. In:
Rubin R, Strayer DS, eds. Rubin’s Pathology: Clinicopathologic
Foundations of Medicine. 6th ed. Philadelphia, PA: Wolters
Kluwer Health | Lippincott Williams &Wilkins; 2012:595.)
