Pulmonary blastomas are a rare aggressive neoplasm comprising 0.25-0.5% of all primary lung tumours . Morphologically they mimic fetal lung tissue before 4 months gestation .
First described by Barnard in 1952 , they have since been divided into three subgroups: classic biphasic pulmonary blastoma, well-differentiated fetal adenocarcinoma -also called monophasic pulmonary blastoma- and pleuropulmonary blastoma of childhood. While well-differentiated fetal adenocarcinoma contains malignant glands and benign appearing mesenchymal tissue and pleuropulmonary blastoma contains malignant glands of embryonal appearance and benign appearing epithelium, classic biphasic pulmonary blastoma contains glands and mesenchymal tissue that are both embryonal and malignant.
In the 1999 and 2004 WHO classifications [4, 5], well-differentiated fetal adenocarcinomas and pleuropulmonary blastomas were separated from the biphasic tumours.
Classic biphasic pulmonary blastoma is now considered as part of the spectrum of sarcomatoid carcinomas.
It typically presents with cough, hemoptysis, dyspnea or chest pain due to tumor impinging on the bronchi or pleura. Forty percent of cases may be asymptomatic . The average age at diagnosis is 40 years with an increased frequency in males (2:1) . Clinical examination may reveal localized reduction in breath sounds or sequalae of cigarette smoking with over 80% of cases associated with a smoking history. Abnormalities in laboratory tests are infrequent and non-specific. Pulmonary blastoma almost always presents as a unilateral, large, well-circumscribed, solitary mass on chest radiograph. Given the often, peripheral nature of these tumors, tissue diagnosis by bronchoscopy only occurs in 25% of cases  but they can often be visualized on thoracic ultrasound with findings correlating well with those seen on CT .
The role of PET-CT in the radiological staging of pulmonary blastoma is unknown with our case demonstrating final pathological staging consistent with that observed using PET-CT. Due to the challenging nature of the histology, a preoperative diagnosis is only obtained in one third of cases  Differential diagnoses must include benign conditions such as hamartoma and pleural fibroma as well as malignant conditions such as other primary or metastatic lung cancers.
Pulmonary blastomas are biphasic tumours that are part of the sarcomatoid carcinoma subgroup , which also include carcinosarcomas (defined as a malignant tumour having a mixture of carcinoma- and sarcoma-containing heterologous elements such as malignant cartilage, bone, or skeletal muscle) and pleomorphic carcinomas (similar tumour without heterologous elements), both histologically resembling adult-type carcinomas and sarcomas.
The epithelial component of classic biphasic blastoma is composed of tubules of glycogen-rich, non-ciliated cells that resemble fetal lung of pseudo-glandular stage of lung development with sub-nuclear and supra-nuclear glycogen vacuoles. The embryonic appearance of the stroma is due to the small size, oval and spindle shape of the cells, and myxoid matrix. Classically this blastematous stroma does not express cytokeratins or pulmonary markers.
Beta-catenin may play a role in tumorigenesis of classic pulmonary blastoma. Its aberrant nuclear/cytoplasmic localization by immunostaining has been reported to be useful in distinguishing classic pulmonary blastoma from a blastomatoid variant of carcinosarcoma and from high-grade fetal type adenocarcinomas .
Surgery is the optimal treatment for localized disease. A mean survival of 33 months was reported in resected cases compared to 2 months in those with un-resected disease. Limited resections do better than pneumonectomies , presumably due to less extensive tumor burden. Larsen  reported a 16% response rate in to chemotherapy in 43 cases of classic biphasic pulmonary blastoma. No agent is known to be more effective than another, but cisplatin is often used given its efficacy with primitive tumors. Most cases have not shown a response to radiotherapy.
Prognosis is poor with two thirds of patients dying within 2 years and only a 16% 5-year survival. Prognosis is determined by size of the tumor at time of diagnosis, with tumors <5 cm doing better. Tumor metastasis and tumor recurrence despite resection both predict a poor prognosis. Unfortunately, 43% of tumors recur within 1 year with a propensity for sites such as brain and mediastinum . Recurrence tends to occur within 1 year after diagnosis or not at all .