13
Respiratory Tract
Fig. 13.61 Moderately differentiated squamous cell carcinoma.
Pulmonary resection (H&E x MP).
Fig. 13.63 Dysplastic squamous epithelium lining a bronchus.
Pulmonary resection (H&E x MP).
Fig. 13.62 Poorly differentiated squamous cell carcinoma. Pulmonary
resection (H&E x MP).
Fig. 13.64 Acinar adenocarcinoma. Pulmonary resection (H&E x MP).
frequently become large302 and tend to occur with pneumonia
due to bronchial obstruction. They are much more likely to
undergo central necrosis with cavitation than are the other types
of lung cancer.304305 The prognosis for squamous cell carcinoma,
stage for stage, is reported to be better than that for adenocar-
cinoma.306 Patients will well-differentiated keratinizing squa-
mous cell carcinomas tend to fare better than those with poorly
differentiated tumors.
Adenocarcinomas have been recognized for many years as
the most common type of lung cancer occurring in females.307,308
In recent years, these tumors have been diagnosed with increas-
ing frequency, to the point that they are now the most com-
monly diagnosed type of lung carcinoma.309-311 Although part of
this increase may result from the broadened WHO definition
of adenocarcinomas299 and the relative increase in the number
of women with lung cancer, as some have suggested,311 other
workers have demonstrated an increased incidence independent
of these factors.309
Histologically, adenocarcinomas may be characterized by
the presence of glandular structures (Fig. 13.64), papillary
structures, a bronchioloalveolar pattern, or histochemically
documented mucin production in tumors with a solid pat-
tern.299 A bronchioloalveolar pattern is defined as growth of
cuboidal or columnar tumor cells along alveolar or fibrovas-
cular septa (Figs 13.65 to 13.68).312 Although adenocarcinoma
may be divided into acinar, papillary, and bronchioloalveolar
subtypes based on the predominant pattern, mixed acinar and
papillary (or bronchioloalveolar) areas frequently occur within
the same tumor.299-313 Ultrastructurally, all types of pulmonary
adenocarcinomas can exhibit various features, including those
reminiscent of goblet cells, bronchiolar (Clara) cells, or type II
pneumocytes.314
The majority of adenocarcinomas occur in the periphery of
the lung315 and may involve the overlying pleura. Scarring is a
common finding in adenocarcinomas315 and has led some to sug-
gest that it represents a predisposing factor for the development
of malignancy.316 In some circumstances, such as diffuse intersti-
tial fibrosis, it is apparent that scarring predates the neoplasm.90
However, the bulk of the literature suggests that in most cases,
the scarring occurs as a response to the tumor.317-319
Bronchioloalveolar carcinoma (BAC) is a heterogeneous
group of neoplasms312,320-324 characterized by a predominant
331
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