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Benign myoepithelioma of the lung: a case report and review of the literature.

REPORT OF A CASE

A 60-year-old woman complained of hoarseness of 6 weeks' duration. The hoarseness proved to be of viral etiology and subsided, but an incidental finding of a right lung nodule was made on a chest radiograph (Figure 1, A). Her past medical history was significant for coronary artery disease, chronic obstructive pulmonary disease, osteoporosis, and varicose veins. She had a hysterectomy 15 years previously. She had been smoking one pack of cigarettes a day for more than 40 years. Her mother had died of lung cancer at the age of 84. The patient was referred to our medical center for further follow-up and possible surgery.

Pulmonary examination revealed diminished breath sounds in the right upper lobe. A computed tomographic scan of the lung showed a 2-cm nodule in the posterior segment of the right upper lobe with no extension to the pleural surface (0.2 cm from pleural surface). No calcification was seen in the lesion. No lesions at the main bronchus were noted. Bronchoscopy was normal. Positron emission tomographic scan showed no uptake of F-18 fluorodeoxyglucose in the nodule, lungs, or mediastinum. The patient underwent video-assisted thoracoscopic surgery, and a wedge resection of the right upper lobe was performed. Frozen section examination showed sheets of small blue cells with a whorling pattern suggestive of a neuroendocrine tumor. The patient recovered well following surgery and had no complications at 2-week follow-up.

METHODS AND RESULTS

A wedge resection of lung tissue that measured 5 x 2.2 x 2 cm was received. The cut section revealed a well-circumscribed, firm, tan, round nodule that measured 2 x 1.5 x 1.5 cm and was located about 0.2 cm from the pleural surface. The resected tissue was fixed in buffered formaldehyde. Immunohistochemical stains, including epithelial markers (cytokeratin and epithelial membrane antigen), muscular markers (smooth muscle actin and desmin), neuroendocrine markers (chromogranin and synaptophysin), neural markers (glial fibrillary acidic protein [GFAP] and S100), and a mesenchymal marker (vimentin), were obtained. Transmission electron microscopy was performed on representative areas from tissue initially embedded in paraffin.

Microscopic sections of the nodule showed small blue cells (Figure 1, B) with a predominantly whorled pattern. There were also areas of a focal reticulum pattern mixed with pink stroma. Most of the cells appeared spindly, with cigar-shaped nuclei and abundant eosinophilic cytoplasm (Figure 1, C). A few plasmacytoid cells were also seen. The nuclei showed dispersed chromatin. Nucleoli were inconspicuous. No mitotic activity, necrosis, or hemorrhage was seen in the tumor.

[FIGURE 1 OMITTED]

Immunohistochemical stains were performed. The tumor cells were not only positive for smooth muscle actin (Figure 2, A) and cytokeratin (Figure 2, B), but also positive for vimentin and GFAE Tumor cells were negative for neuroendocrine markers including synaptophysin and chromogranin as well as for S100, epithelial membrane antigen, and desmin. Ultrastructurally, medium-sized cells were identified in a cohesive pattern, but no well-defined intercellular junctions were seen (Figure 2, C). The cells showed round to ovoid nuclei with one to several nucleoli and variable amounts of cytoplasm. In the cytoplasm, undulating filaments that were located close to the nucleus were most consistent with tonofilaments. Myofilaments, primarily present in the periphery of the cells, were arranged in bundles and showed occasional dense bodies or spindle densities (Figure 2, C). These were associated with areas of membrane thickening.

[FIGURE 2 OMITTED]

COMMENT

Myoepitheliomas have been described more commonly in salivary glands. (1) Other sites include soft tissue, breast, palate, lip, cheek, gingiva, and lacrimal and buccal glands. (1) In the lung, myoepithelioma is a rare tumor. In the English language literature, myoepithelioma of lung may have been used as a vague and confusing tern to describe a pulmonary lesion of a myoepithelial origin. Several so-called myoepitheliomas were actually malignant tumors, (2, 3) and another 2 myoepitheliomas were considered benign (4, 5) (Table). We therefore feel that benign myoepithelioma is the best term to define the current lesion to avoid confusion with malignant myoepithelial lesions in the lung. Although the benign myoepithelioma in the current case report shares a similar light-microscopic appearance and positive staining reaction for smooth muscle actin with the 2 previously reported myoepitheliomas of a benign nature, (4, 5) the current case has at least 4 divergent findings. First, the benign myoepithelioma in the current case was positive for cytokeratin, whereas the previous 2 lesions were negative for cytokeratin. (4, 5) Positive stains for both smooth muscle actin and cytokeratin in the current case strongly support the fact that the benign myoepithelioma has muscular and epithelial differentiation, thus distinguishing it as myoepithelioma. Second, positive stains for smooth muscle actin and cytokeratin in the current case are further supported by ultrastructural identification of myofilaments and tonofilaments, respectively. In contrast, one previous myoepithelioma only showed myofilaments, (4) and in the other previous myoepithelioma case (5) no electron microscopy was performed. Third, the cells from the benign myoepithelioma were also positive for GFAP; myoepithelioma may be GFAP positive. (1) No staining for GFAP was reported in the previous 2 cases. (4, 5) Fourth, S100 stain was negative in our lesion but positive in the 2 previous cases. (4,5) Because S100 protein is not a uniformly present antigen in normal myoepithelial cells, (1) lack of reactivity of the benign myoepithelioma cells does not exclude the diagnosis of myoepithelioma.

Positron emission tomographic scanning has revolutionized evaluation and staging of benign and malignant pulmonary tumors. (6) Because of the recent advent of this imaging method and because of the rarity of some types of pulmonary nodules, the fluorodeoxyglucose uptake of many such tumors is unknown. This patient gave us the opportunity to perform a positron emission tomographic scan on a benign pulmonary myoepithelioma for the first time. The scan was performed by injecting a standard dose of 14.6 mCi F-18 fluorodeoxyglucose isotope and then reconstructing the image in multiple planes using attenuated and nonattenuated corrections. No fluorodeoxyglucose accumulation was noted in the nodule or mediastinum. This coincides well with the benign histologic findings.

In summary, benign myoepithelioma can occur rarely in the lung, and it is important to consider this entity in the differential diagnosis of lung nodules, especially when using fine-needle aspiration biopsies. Electron microscopy and immunohistochemical stains should be performed on all such cases for accurate diagnosis of this unusual pulmonary neoplasm.
Comparison of Cases of Myoepithelioma and Myoepithelial Carcinoma
Reported in the Literature *

 Location
Reference Term Used Cases in Lung LM Features

Current Benign 1 Periphery Benign (1.7 cm)
 case myoepithelioma
4 Myoepithelioma 1 Periphery Benign (3.3 cm)
5 Mydepithelioma 1 Periphery Benign (2.5 cm)
2 Myoepithelioma 2 Central Malignant (3.8
 and 6 cm)
3 Myoepithelioma 1 NA Malignant
 (unknown size)
7 Myoepithelial 1 Central Malignant (6.5 cm)
 carcinoma

Reference Cell Markers EM Metastasis

Current Actin (+) T, M No
 case Keratin (+)
 S100 (-)
 GFAP (+)
4 Actin (+) M No
 Keratin (-)
 S100 (+)
5 Actin (+) NA No
 Keratin (-)
 S100 (+)
2 Actin (+/+) T, D Yes
 Keratin (+/-)
 S100 (+/-)
3 NA NA Yes
7 Actin (+) T, D Yes
 Keratin (+)
 S100 (+)

* LM indicates light microscopy; EM, electron microscopy; GFAP, glial
fibrillary acidic protein; T, tonofilaments; M, myofilaments; NA, not
available; and D, desmosomes.


References

(1.) Dardick I. Myoepithelioma: definitions and diagnostic criteria. Ultrastruct Pathol. 1995;19:335-345.

(2.) Higashiyama M, Kodama K, Yokuchi H, et al. Myoepithelioma of the lung: report of two cases and review of the literature. Lung Cancer. 1998;20:47-56.

(3.) Sekine I, Kodama T, Yokose T, et al. Rare pulmonary tumors--a review of 32 cases. Oncology. 1998;55:431-434.

(4.) Strickler JG, Hegstrom J, Thomas MJ, et al. Myoepithelioma of the lung. Arch Pathol Lab Med. 1987;111:1082-1085.

(5.) Cagirici U, Sayiner A, Inci I, et al. Myoepithelioma of the lung. Eur J Cardiothorac Surg. 2000;17:187-189.

(6.) McCain TW, Dunagan DP, Chin R Jr, et al. The usefulness of positron emission tomography in evaluating patients for pulmonary malignancies. Chest. 2000; 188:1610-1615.

(7.) Muira K, Harada H, Aiba S, et al. Myoepithelial carcinoma of the lung arising from bronchial submucosa. Am J Surg Pathol. 2000;24:1300-1304.

Accepted for publication May 9, 2001.

From the Departments of Pathology (Drs Veeramachaneni, Gulick, Zhang, and Herrera), Surgery and Positron Emission Tomographic Imaging (Drs Halldorsson and Van), Louisiana State University Health Sciences Center, Shreveport, La.

Reprints: Ping L. Zhang, MD, PhD, Department of Pathology, 1501 E Kings Highway, Shreveport, LA 71130.
COPYRIGHT 2001 College of American Pathologists
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2001 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:Veeramachaneni, Ravindra; Gulick, Janis; Halldorsson, Ari O.; Van, Thanh T.; Zhang, Ping L.; Herrera
Publication:Archives of Pathology & Laboratory Medicine
Date:Nov 1, 2001
Words:1392
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