Pulmonary blastoma (ORPHA:64741)
A biphasic primary lung neoplasm, belonging to the group of sarcomatoid lung carcinomas (SLCs). The tumor contains both an epithelial well-differentiated component, showing tubular architecture resembling the normal fetal lung, and a mesenchymal undifferentiated stroma with a so-called ''blastema-like'' configuration that resembles an embryonic lung.
Epidemiology
PB is a rare tumor, accounting for less than 0.25% of all primary malignant lung tumors, with only around 350 cases having been reported in the literature so far. PB occurs almost exclusively in adults and has a peak incidence in the fourth decade of life (earlier than other forms of SLC), with a marked female predominance (70% of cases) and frequent association with tobacco smoking.
Clinical description
Symptomatic patients present with nonspecific respiratory manifestations (cough, hemoptysis and chest pain). Other features may include dyspnea, fever, weight loss, and recurrent pneumonia. However, up to 40% of patients may be identified presymptomatically after a chest radiograph for another indication. PBs are usually well-demarcated solitary tumors (average size 10 cm) with cystic and necrotic features and are often located in the peripheral lung. Common sites of metastases include the brain, lymph nodes and liver.
Etiology
Little is known about the pathogenesis and histogenesis of PB. Molecular studies indicate that mesenchymal and epithelial components are derived from a single precursor cell. Mutations in several genes (including TP53, CTNNB1 and EGFR) may be identified in some PB tumors.
Diagnostic methods
Clinical laboratory and imaging studies are nonspecific and definitive diagnosis of PB requires identification of both the epithelial and mesenchymal components of the tumor, through histological studies on a resected specimen. Bronchoscopy and fine needle biopsy have been useful for diagnosis in some cases.
Differential diagnosis
The differential diagnosis should include other forms of SLC (pleomorphic carcinoma, spindle cell carcinoma, giant cell carcinoma, carcinosarcoma and adenocarcinoma (particularly fetal adenocarcinoma); see these terms). PB also has to be distinguished from the childhood tumor pleuropulmonary blastoma (see this term).
Management and treatment
In many cases, the tumor is initially thought to be a bronchogenic carcinoma. Complete surgical resection with mediastinal lymph node dissection ensures both diagnosis and therapy. Adjuvant treatment, mostly consisting of radiotherapy, has been reported in a few cases, following incomplete resection, or in patients with N2 mediastinal involvement. For unresectable tumors, chemotherapy may be based on protocols used for sarcomas, including doxorubicin and ifosfamide.
Prognosis
PB is an aggressive tumor and the prognosis has historically been reported as being poor: 5-year survival rates for patients with stage I disease were around 30%. In most recent reports, survival -adjusted by stage- is better than that for non-small cell lung cancer, especially in completely resected cases. Recurrences (occurring in 30-40% of patients) and metastases are common.

                            Last update: 
                            November 2012


                            - Expert reviewer(s): 
                            Pr Nicolas GIRARD