EMC has mainly been reported in the areas of orthopedics, neurosurgery, and otolaryngology [
1]. As with our case, the characteristic features of well-circumscribed, multilobulated configuration with incomplete fibrous septae, oval to spindle shaped cells arranged in short anastomosing strands embedded in abundant myxoid matrix and typical histochemical findings favored the diagnosis of EMC [
2]. Since the lesion located at the periphery of the lung, fine needle aspiration biopsy (FNAB) should be initially done to help diagnosis. Although cytologic characteristics are not decisive for diagnosis, the presence of intranuclear cytoplasmic inclusions, grooves and cytoplasmic vacuolization could be suggestive to EMC diagnosis [
3]. S-100 protein was initially found in most EMC, but recent studies proved that less than 20 % of EMC are S-100 positive [
4]. In some cases of EMC, there is neuroendocrine differentiation [
5]. A specific chromosomal translocation t(9;22)(q22;q12) leading to a fusion gene, EWS-CHN has been found in 75 % EMC cases [
6], and another fusion gene TAF2N-CHN caused by t(9;17)(q22;q11.2) translocation has recently been identified [
5]. Although primaries should not have difficulty in diagnosis for experienced pathologists, the morphologic differential diagnosis in our case are parachordoma, chordoma, soft tissue chondroma, extraskeletal mesenchymal chondrosarcoma,as well as pulmonary metastases of EMC. Parachordoma is an indolent soft tissue tumor predominantly in the extremities and trunk, occasionally in the chest wall. The diagnosis is excluded because there were no typical histopathologic and immunohistochemical features of parachordoma such as plasma cell-like appearance of the tumor cells with chondrometaplasia myoepithelium, and expression of cytokeratin, and EMA. Chordoma appears as lobulated tumors, with cord pattern tumor cells scattering within abundant myxoid stroma. The diagnosis is ruled out by a lack of physaliferous cells, and no expression of cytokeratin. Soft tissue chondroma composed of small cells with hyaline cartilage lobule which lies near the joints of extremities, and S-100 is uniquely positive. Extraskeletal mesenchymal chondrosarcoma arising in lung [
7], chest wall, pleural and mediastinum has been reported. The lack of small undifferentiated cells surrounding narrow vascular spaces in a haemangiopericytoid (haemangiopericytoma-like) pattern with mature cartilage island would exclude extraskeletal mesenchymal chondrosarcoma. As lung is the most frequent site of metastases in EMC, it is necessary to differetiate primary EMC in lung from lung metastases of EMC. However, it was not difficult to exclude lung metastases of EMC originated in the other parts of the body after comprehensive clinical evaluation and CT scan, with particular attention to the distal parts of the extremities. There was not any evidence of tumor in the body other than in the lung of the patient. Extraosseous (extramedullary) plasmacytoma (EMP) is defined as localized plasma cell neoplasms arising in tissues other than bone, and EMP in lung has been reported [
8]. In our case, there are abundant plasma cells and aggregated lymphocytes in tumor fibrous septae and adjacent lung tissue which might be the anti-tumor reaction of immune system. As to EMP, the neoplastic cells are similar to normal plasma cells with very few lymphocytes. Last, our case should also be differentiated from primary pulmonary sarcomas. Pulmonary myxoid liposarcoma is multinodular-architecture in myxoid stroma with Vimentin and S-100 positive which is similar to EMC, however, lack of lipoblasts and plexiform capillary network exclude the diagnosis [
9]. Immunostains can be helpful to rule out rhabdomyosarcoma, leiomyosarcoma. Primary and metastatic chondrosarcoma of lung have been documented, and the multilobular neoplasm with chondroid and myxoid matrix which is positive to Vimentin and S-100, negative for epithelial markers might cause the confusion with EMC [
10]. In this case, absence of predominant chondromatous lesion helps to exclude chondrosarcoma. Pulmonary carcinosarcoma is ruled out for lack of carcinomatous component [
11].
Although EMC is most common in the soft tissues of the extremities, in fact, the primary site can be anywhere in the body [
1]. To our knowledge, no case of EMC arising in lung has been reported to date. Primary EMC of the pleura has been described by Goetz et al. [
12]. From the CT scan, a parenchymal mass of left upper lobe can be found with distinct margin from the intact visceral pleura, which were also proved by microscopic examination on cut section of tumor. We suggest that the origin might be primitive mesenchymal cell, or associated with the tracheobronchial cartilage [
13,
14].
Anemia is one of the characteristics in this patient which has not been reported previously in EMCs. Patients afflicted with malignancy often develop anemia, and some cytokines, particularly TNF-α,TGF-β,IFN-β, IL-1,are found increasing in many malignant diseases [
15,
16]. The function of these cytokines is related to retention of iron in the reticuloendothelial system, gastrointestinal tract and liver and exert inhibitory effects on erythroid precursors [
17]. As in our case, expression of IFN-β in tumor cells, significant in excessive type IFN signaling, inhibits erythropoiesis through decreased Bcl-XL expression level and enhanced apoptosis of erythroblasts [
18]. Also, negative bone marrow cytology rules out occurrence of primary hematological malignancies, such as multiple myeloma. It is intriguing that the anemia was corrected just after the removal of the tumor, suggesting that the cause of anemia relies on the tumor itself.
EMC shows a tendency to affect patients beyond their fifth decade [
19]. EMC was initially viewed as a low-grade sarcoma with prolonged and indolent clinical course, but recent studies found its unfavorable prognosis with high rate of recurrence and metastases [
20]. Significant in the past history was that our 51-year-old patient had a left lung nodule examined by routine chest x-ray check for around 10 years, which was in accordance with those previous reports. Since EMC has a high rate of recurrence and metastases, and the death caused by tumor often occurs in a long postoperative period, sometimes more than 10 years after diagnosis, so we suggest that frequent and long-term follow up is needed for our patient.