Primary tracheal neoplasms are very uncommon but are usually malignant in adults and benign in children. They present with symptoms that mimic other conditions, so there is often diagnostic delay, and by the time the diagnosis is certain, the cancer is in an advanced stage, which affects the prognosis.
Several risk factors correlate with increased risk for tracheal squamous cell carcinomas such as smoking, exposure to alternative carcinogens such as inhaled hydrocarbons, and history of prior lung cancer. There are no identified risk factors for adenoid cyst carcinoma.
The incidence of tracheal cancers is 2.6 new cases per 1000000 people per year. It accounts for 0.1% to 0.4% of newly diagnosed cancers annually. Squamous cell carcinoma occurs more frequently in males in their sixth and seventh decades, while adenoid cystic cancer is distributed equally between both sexes and occurs in fourth and fifth decades.
Tracheal cancer may arise from the epithelial cells, mesenchymal structure or salivary glands. It is malignant in 90% of cases in adults, while only 20 to 30% of cases are malignant in children.
Squamous cell carcinoma is the most common type of tracheal carcinoma followed by adenoid cystic carcinoma. Other types include mucoepidermoid, small cell carcinoma, neuroendocrine carcinoma, adenocarcinoma, large cell carcinoma, sarcomas, fibroma, pleiomorphic adenoma, and others. Squamous cell carcinoma has lung and mediastinal metastases in a third of cases at the time of diagnosis; these lesions may be exophytic or ulcerative. By contrast, adenoid cystic carcinoma usually grows slowly over several years.
Primary tracheal cancers may present with signs and symptoms of upper airway obstruction (dyspnea, stridor, and wheezing), cough and hemoptysis from mucosal irritation, or symptoms related to invasion of adjacent structures and lead to dysphagia or hoarseness due to recurrent nerve palsy. Squamous cell carcinoma usually presents with hemoptysis and is diagnosed within four to six months of symptoms onset, while adenoid cystic carcinoma is slowly growing and presents with dyspnea and wheezing.
Several factors play a role in missed and delayed diagnosis. First, the non-specific symptoms like a cough, hemoptysis, dyspnea, and wheezes are also present in more common diseases like COPD, asthma, bronchitis or other infections. Second, the tracheal lumen is usually large with a significant reservoir, and symptoms of obstruction do not occur until the mass occupies more than 50 to 75% of lumen diameter. Third, adenoid cystic cancer and other benign tumors grow slowly, and symptoms progress slowly over a period of months or years.
A high index of suspicion for tracheal cancer should be raised when respiratory symptoms are not responding to medical therapy.
Initial evaluation starts with a chest radiograph to rule out other pathologies. Visualization of a tracheal mass or narrowing only occurs in a minority of cases. Computed tomography of the chest with recent advances in imaging techniques and three-dimensional reconstruction may allow for early detection of cancer, degree, and pattern of invasion. The imaging study will also reveal if the cancer is localized or has distant metastasis, which may help determine the type of treatment.
Bronchoscopy evaluation provides the opportunity for direct visualization of the mass and direct tissue biopsy. Use of endobronchial ultrasound allows for better evaluation of the extent of wall invasion and enables detection of paratracheal tumors invading the trachea.
Surgical resection is the treatment of choice for malignant tracheal cancer whenever possible. Usually, this is followed by adjunctive therapy with radiation or chemotherapy. Proper surgical resection improves prognosis, symptoms, and quality of life. Five-year survival is 50% for patients treated with surgery while it is only 10% in patients who are not surgical candidates. Several factors play a role before deciding surgical intervention such as age, comorbidities, neck mobility, length of cancer extent and degree of invasion.
Surgical intervention is not the recommendation in patients with tumors involving more than 50% of the tracheal length because of the correlation with increased mortality. Other contraindications for surgery include respiratory failure, oral corticosteroids dependence, invasion of heart or aorta, distant metastasis, the involvement of multiple lymph nodes groups and previous radiation therapy with a high dose greater than50 Gy.
Adjunctive therapy with radiation is recommended for all types of tracheal cancers that are locally advanced after surgical resection but not used for tumors in very early stages. In patients with squamous cell carcinoma, radiotherapy correlates with improved survival even in the absence of cancer cells in the resected margins. Although adenoid cystic carcinoma is less radiosensitive, however, radiation is associated with better outcomes and decreased recurrence rates. In nonsurgical candidates, radiotherapy is considered the first line of treatment and is a palliative option in advanced disease.
The literature lacks randomized controlled trials examining chemotherapy in patients with tracheal cell cancers, and the role of chemotherapy remains unclear. However, cisplatin-based chemotherapy is used in combination with radiotherapy in unresectable disease or after surgery.
In poor surgical candidates or with advanced unresectable tumors, interventional procedures such as stent placement are sometimes necessary, in combination with radiation as palliative therapy. Stents are also used in emergencies in patients presenting with complete or significant obstruction of airways as a bridge to surgery.
No established staging system is specific for tracheal cancers. Some investigators employ the tumor, nodes, and metastasis (TNM) staging system for disease staging.
Five-year survival of primary tracheal cancer in a large population-based registry was 27%. Adenoid cystic carcinomas carry a better prognosis than squamous cell carcinomas with a significant difference in 5-year survival between both tumors (74% vs. 12%). The favorable prognosis for adenoid cystic carcinomas reflects the slower growth and a more prolonged natural history of this tumor. Early diagnosis and definitive surgical therapy before local or distant spread of cancer is associated with favorable prognosis and increased survival. Five-year survival was 4%, 25% and 47% in distant metastasis, regional disease, and localized cancers respectively in an extensive population-based registry.
Complications related to the primary cancer growth and invasion of local organs include airway obstruction, dysphagia, and hoarseness. Postoperative complications include failed anastomotic healing, infections, cancer recurrence and reduced quality of life especially with resection of large segments of the trachea leading to significant limitation in neck extension.
Primary tracheal carcinomas are rare and require a high index of suspicion for diagnosis especially in the absence of response to treatment of other alternative diagnoses such as COPD, asthma or infections. Squamous cell carcinoma and adenoid cystic carcinoma are the most common histopathological types. Computed tomography is the imaging modality of choice for diagnosis and bronchoscopy provides the chance for direct visualization and biopsy of the mass. Surgery with complete resection of the tumor should be performed whenever possible as it correlates with increased 5-year survival. Adjunctive radiotherapy is helpful in most cases. In advanced unresectable diseases, radiation and bronchoscopic interventions such as stenting of the trachea serve as palliative therapy.
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