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Sarcomatoid Carcinoma of the Lung: Histologic Criteria and Common Lesions in the Differential Diagnosis

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CONTEXT: Sarcomatoid carcinoma of the lung is a subset of poorly differentiated non-small cell lung cancers that are diagnostically challenging because they are uncommon, may reveal little of their parent cell of origin, and overlap morphologically with other anaplastic epithelioid and spindle cell tumors that can be primary in, or metastatic to, the lung and pleura. OBJECTIVE: To review the current histologic classification and diagnostic criteria that identify the 5 subtypes of sarcomatoid carcinoma of the lung and to discuss the most common tumors in the differential diagnosis. DESIGN: Published classification systems from the World Health Organization and pertinent peer-reviewed articles indexed in PubMed (National Library of Medicine) form the basis of this review. CONCLUSIONS: Identification of sarcomatoid carcinoma of the lung requires knowledge of specific histologic criteria that define the 5 subgroups, targeted immunohistochemical studies, and correlation with chest imaging to assess distribution of disease and to avoid misdiagnosis.

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									                           Sarcomatoid Carcinoma of the Lung
          Histologic Criteria and Common Lesions in the Differential Diagnosis
                                                  Teri J. Franks, MD; Jeffrey R. Galvin, MD

● Context.—Sarcomatoid carcinoma of the lung is a subset                     Design.—Published classification systems from the
of poorly differentiated non–small cell lung cancers that                  World Health Organization and pertinent peer-reviewed
are diagnostically challenging because they are uncom-                     articles indexed in PubMed (National Library of Medicine)
mon, may reveal little of their parent cell of origin, and                 form the basis of this review.
overlap morphologically with other anaplastic epithelioid                    Conclusions.—Identification of sarcomatoid carcino-
and spindle cell tumors that can be primary in, or meta-                   ma of the lung requires knowledge of specific histologic
static to, the lung and pleura.                                            criteria that define the 5 subgroups, targeted immuno-
   Objective.—To review the current histologic classifica-                  histochemical studies, and correlation with chest imag-
tion and diagnostic criteria that identify the 5 subtypes of               ing to assess distribution of disease and to avoid misdi-
sarcomatoid carcinoma of the lung and to discuss the most                  agnosis.
common tumors in the differential diagnosis.                                 (Arch Pathol Lab Med. 2010;134:49–54)


P  oorly differentiated non–small cell carcinomas of the
     lung with sarcoma-like differentiation (spindle and/
or giant cell) or a component of sarcoma (malignant bone,
                                                                           ond, regarding the histogenetic mechanisms that would al-
                                                                           low conventional subtypes of lung cancer to coexist with
                                                                           malignant spindle and/or giant cell elements and sarcoma.
cartilage, or skeletal muscle) are unified within the um-                      For the past 25 years, the World Health Organization
brella term sarcomatoid carcinoma by the World Health Or-                  has been under constant pressure to change the classifi-
ganization. Five subtypes are recognized: pleomorphic                      cation of sarcomatoid tumors of the lung. This has been
carcinoma, spindle cell carcinoma, giant cell carcinoma,                   driven in part by the histologic heterogeneity of the tu-
carcinosarcoma, and pulmonary blastoma.1 Sarcomatoid                       mors and in part by our evolving understanding of their
carcinomas are rare, comprising approximately 1% of all                    histogenetic origins. The 1981 World Health Organiza-
lung malignancies.2,3 Patients are predominantly male                      tion’s Histological Typing of Lung Tumours 12 recognized
smokers, with a mean age at diagnosis of 65 years; cough                   spindle cell carcinoma as a variant of squamous cell car-
and hemoptysis are the most common presenting symp-                        cinoma; giant cell carcinoma as a variant of large cell car-
toms, the clinical course is aggressive, and as with con-                  cinoma; and carcinosarcoma and pulmonary blastoma as
ventional non–small cell lung carcinoma, stage is the most                 miscellaneous malignant tumors. Classifications organiz-
important prognostic indicator.2,4–11 Pulmonary blastoma is                ing these lesions as monophasic or biphasic, with biphasic
an exception in that it demonstrates an equal sex ratio and                examples further subclassified as homologous or heterol-
has a mean age at diagnosis of 35 years.6                                  ogous, were subsequently proposed and
								
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