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.