OTHER NEOPLASMS OF THE LUNG
Uncommon
malignant tumors of the lung include bronchial carcinoid and salivary gland
tumors of adenoid cystic carcinoma and mucoepidermoid carcinoma. Bronchial
carcinoid tumors account for 1% to 2% of all lung malignancies and 20% of all
carcinoid tumors. The annual rates in men and women are 0.52 and 0.89,
respectively, per 100,000 population. These tumors are characterized by growth
patterns that suggest neuroendocrine differentiation. Bronchial carcinoids are
classified as typical or atypical. Typical carcinoid tumors are low-grade tumors
with fewer than 2 mitoses per 2 mm2 (10 high-power microscopic fields) and no
necrosis. Atypical carcinoids are intermediate grade neuroendocrine tumors with 2 to 10 mitoses per 2 mm2 or foci of
necrosis. Typical carcinoid tumors are about four times more common than
atypical carcinoids. There is no clear relationship to smoking.
Approximately 75% of these tumors arise in the central
airways. The usual symptoms are cough, wheeze, hemoptysis, and recurrent
pneumonia. One-fourth are peripherally located and are usually asymptomatic or
present as an obstructive pneumonia. Five percent may present with an endocrine
syndrome such as carcinoid syndrome, Cushing syndrome, or acromegaly.
Centrally located tumors are likely to cause bronchial
obstruction with atelectasis, lobar collapse, or pneumonia on chest radiography
or computed tomography (CT) scan. Cavitation and pleural effusion, unless
related to pneumonia, are rare. The CT scan may show an intraluminal tumor in
the central airways. Carcinoid tumors are more commonly smooth bordered but may
also be lobulated and are less likely to have irregular borders.
Bronchoscopy is able to visually identify an endobronchial
lesion in a majority of cases because 75% are centrally located. The pink to
red vascular-appearing mass is typical. Biopsy is frequently diagnostic.
Bleeding may be a little more prominent than with non–small cell lung cancer,
but serious bleeding complications are uncommon. Sputum cytology and bronchial
brushings are usually nondiagnostic. Transthoracic needle biopsy may be
diagnostic, but occasionally carcinoid tumor and small cell lung cancer have
been confused histologically on small samples from needle biopsy.
The treatment of choice is surgical resection for stage
I, II, and IIIA disease (the staging system is same as for non–small cell lung
cancer). The 10-year survival with typical carcinoid tumors is 80% to 90%.
Survival of those with atypical tumors is significantly less but still
approximately 50% at 5 years and depends on the stage of disease at the time of
diagnosis. Carcinoid tumors, both typical and atypical, are more chemoresistant
and radiotherapy resistant than non–small cell lung cancer. Nevertheless,
concurrent chemoradiotherapy is the treatment of choice for patients with
unresectable stage IIIA/B disease. Stage IV disease is very chemoresistant, but
the somatostatin analog octreotide is effective at controlling the symptoms of
carcinoid syndrome (flushing and diarrhea) and may impact survival.
Salivary gland tumors of the tracheobronchial tree are
histologically similar to their counterparts in the salivary glands. The two
most common airway tumors are adenoid cystic carcinoma (cylindroma) and
mucoepidermoid carcinoma; both are less common than carcinoid tumors. There is no clear association of
these tumors with smoking. Adenoid cystic carcinoma causes fewer than 1% of all
lung tumors, and the vast majority of cases originate intraluminally in the
trachea, mainstem, or lobar bronchi. These tumors are typically very slow
growing, and the symptoms and presentation are similar to those of centrally
located carcinoid tumors. The chest radiograph is frequently normal because of
the central endoluminal location of the tumor, but CT usually identifies the
tumor. Bronchoscopy is the most common method of diagnosis.
Surgical resection is the treatment of choice, but
multiple local recurrences are common before developing distant metastases. The
5- and 10-year survival rates for resected adenoid cystic carcinoma are
approximately 70% and 60%, respectively, compared with unresectable disease, in
which the 5- and 10-year survival rates are 50% and 30%, respectively.
Mucoepidermoid carcinomas account for fewer than 1% of
lung tumors. They form a significant proportion of endobronchial tumors in
children. These tumors tend to occur centrally in the tracheobronchial tree.
Tumors are divided into low-or high-grade types on the basis of histology.
High-grade tumors are rare and have a significantly worse prognosis. The
clinical and radiographic presentations of this tumor are similar to those of
adenoid cystic carcinomas, and bronchoscopy is the most common method of
diagnosis. The treatment of choice is surgical resection. Low-grade tumors
metastasize in 5% or fewer of cases. High-grade tumors are treated similarly to
non–small cell lung cancer and have a poor prognosis. The overall survival rate
for resected mucoepidermoid carcinoma is 80% to 90% at 5 years. Patients with
mucoepidermoid carcinoma have better survival than those with adenoid cystic carcinoma.
