Squamous cell
carcinoma (SCC) is defined as a malignant epithelial tumor showing
keratinization or intracellular bridges (or both) arising from bronchial
epithelium. Previously, SCC, sometimes called epidermoid carcinoma, was
the most common cell type, but that has changed in the past 1 or 2 decades in
the United States, parts of Western Europe, and Japan. Currently, SCCs account
for 20% of all lung cancers in the United States (http://seer.cancer.gov). The
vast majority of SCC occurs in smokers. Recent Surveillance, Epidemiology and
End Results (SEER) data report that SCC accounts for 24% of all cancers in men
versus 16% in women. The recent decrease in SCC and increase in adenocarcinoma
histology has been attributed to the change in the cigarette, from nonfilter to
filter, and the decrease in tar. About 60% to 80% of these cancers arise
centrally in mainstem, lobar, or segmental bronchi, but they may present as a
peripheral lung lesion.
SCC arises from the bronchial epithelium, and it is thought that the airway abnormality progresses through
a series of changes from hyperplasia to dysplasia to carcinoma in situ, which
is classified by World Health Organization as preinvasive and a precursor to
SCC. Varying degrees of dysplasia have been associated with cumulative genetic
alterations, but the critical genetic change(s) before developing frank cancer
is still uncertain.
Because of the tendency to occur centrally in the
airway, SCC presents more commonly with hemoptysis, new or change in cough,
chest pain, or pneumonia caused by bronchial obstruction. The usual
radiographic presentation is a central mass or obstructing pneumonia with or
without lobar collapse. About 10% to 20% of SCCs present as peripheral lesions.
Cavitation may occur in 10% to 15% of all SCCs and is the most common histology
associated with cavitation. The cavities are usually thick walled. Cavitation
in the lung may also be caused by obstructive pneumonia and abscess formation.
Sputum cytology has the highest diagnostic yield with
this cell type because of the predominant central location. Bronchoscopy with
brushings and biopsy are diagnostic in more than 90% of SCCs when the cancer is
visible endoscopically. The yield for peripheral lesions that are
endoscopically negative is significantly less and depends on the size of the
tumor. For lesions smaller than 2 cm in diameter, transthoracic needle
aspiration has the highest diagnostic yield if a tissue diagnosis is required
before surgical resection.
SCC in situ (pre invasive lesion) has an unpredictable
course, and the treatment is a topic of current debate. Surgery is the
treatment of choice for early-stage disease (stage I or II). Combination
chemotherapy and radiotherapy are recommended for good performance score
patients with unresectable stage III A or B disease. Stage IV (metastatic
disease) is generally treated with systemic chemotherapy, but treatment is
noncurative (palliative).
It was previously believed that SCC was more
slow-growing than other cell types, but recent analysis of a large international
database that controlled for stage of disease does not demonstrate definite
survival benefit of SCC versus other non–small cell histologies. In the past,
SCCs have been treated the same as all other non–small cell histologies, but
recent data show that optimal treatment depends on specific typing.
