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    SARCOMATOID CARCINOMA
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    Sarcomatoid carcinoma is a general term that includes pleomorphic carcinoma, carcinosarcoma, and pulmonary blastoma. For this reason, it is best to use the specific term for these entities whenever possible rather than the general term. This also may avoid any confusion with a true sarcoma. These tumors are rare accounting for less than 1% of all lung cancers.93 There are no major changes in the terminology or diagnostic criteria for these tumors since the 2004 Classification. One new aspect is the recommendation for molecular testing according to known genetic abnormalities associated with histologic components (i.e., tumors with an adenocarcinoma component should be tested for EGFR mutation and ALK rearrangement). The diagnoses of pleomorphic, spindle cell, or giant cell carcinoma cannot be made on small biopsies or cytology, and recommendations for diagnostic terminology in these types of specimens are discussed above. It is very difficult to diagnose carcinosarcoma or pulmonary blastoma in small biopsies and cytology, but if material is obtained that fulfills diagnostic criteria, it is possible. Prognosis for all these tumors is poor.

    Pleomorphic carcinoma is a poorly differentiated NSCC namely a squamous cell carcinoma, adenocarcinoma, or undifferentiated NSCC that contains at least 10% spindle and/or giant cells or a carcinoma consisting only of spindle and giant cells. The prevalence of KRAS (in up to 38% of cases) 94 ;  95 and EGFR mutations (in up to 25% of cases) 96; 97 ;  98 partially reflects the tumor components (i.e., adenocarcinoma), patient ethnicity, and smoking habits.99

    Spindle cell carcinoma consists of an almost pure population of epithelial spindle cells, with no differentiated carcinomatous elements.

    Giant cell carcinoma consists almost entirely of tumor giant cells (including multinucleated cells), with no differentiated carcinomatous elements. Definite diagnosis may only be made on a resected tumor. The specific histological components should be mentioned in the diagnosis.

    Carcinosarcoma is a malignant tumor that consists of a mixture of NSCLC (typically squamous cell carcinoma or adenocarcinoma) and sarcoma-containing heterologous elements, such as rhabdomyosarcoma, chondrosarcoma, and osteosarcoma. Carcinosarcomas are clonal tumors developing through sarcomatoid change in a carcinoma.102TP53 mutations are often present in carcinosarcoma, whereas KRAS mutations occur less frequently, and EGFR mutations are very uncommon. 

    Pulmonary blastoma is a biphasic tumor that consists of fetal adenocarcinoma (typically low grade) and primitive mesenchymal stroma. Foci of specific mesenchymal differentiation (osteosarcoma, chondrosarcoma, or rhabdomyosarcoma) may also be present but are not required for the diagnosis. Pulmonary blastoma and well-differentiated fetal adenocarcinoma (a putative precursor lesion) are frequently associated with missense mutations in exon 3 of CTNNB1, responsible for activation of the Wnt pathway through aberrant nuclear/cytoplasmic localization of β-catenin protein.TP53 mutation and both p53 and MDM2 protein accumulation are occasionally detected in pulmonary blastoma. 

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