Ann Thorac Surg 1999;68:1863-1865
© 1999 The Society of Thoracic Surgeons
Case Reports
Basaloid carcinoma of the thymus
Osamu Kawashima, MDa,
Mitsuhiro Kamiyoshihara, MDa,
Shuji Sakata, MDa,
Terumasa Kurihara, MDa,
Susumu Ishikawa, MDa,
Yasuo Morishita, MDa
a Department of Surgery, National Sanatorium Nishigunma Hospital, Gunma, Japan
Address reprint requests to Dr Kawashima, Department of Surgery, National Sanatorium Nishigunma Hospital, 2854 Kanai, Shibukawa, Gunma 377-8511, Japan
e-mail: kawasimao{at}nngh.hosp.go.jp
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Abstract
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A 58-year-old man was found to have a basaloid carcinoma of the thymus, initially detected as an abnormal shadow on chest radiograph. The patient underwent resection followed by radiotherapy, and has survived 25 months without recurrence. Although this rare tumor may be related to multilocular thymic cyst, its pathogenesis is obscure. We discuss clinicopathologic features of our case and others.
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Introduction
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Squamous cell carcinoma and lymphoepithelioma-like carcinoma are the most common variants of the thymic carcinomas, while basaloid carcinoma is rare. We present a case of basaloid carcinoma of the thymus and discuss a review of the clinicopathologic features, including previously reported cases.
An asymptomatic 58-year-old man was found to have an abnormal shadow in the mediastinum during routine screening chest radiography, and was transferred to our hospital for further evaluation. His past history was noncontributory. On admission, physical examination revealed normal findings. Laboratory data were within normal limits, including serum concentrations of such tumor markers as carcinoembryonic antigen, squamous cell carcinoma antigen, neuron-specific enolase, and alpha-fetoprotein. Chest roentogenograms and computed tomograph (CT) revealed a partially cystic, heterogeneous anterior mediastinal mass, 6.0 x 5.0 cm in size.
Fine-needle aspiration of the mass yielded material insufficient for a diagnosis. As malignant tumor was a possibility, the mass was excised completely through a median sternotomy. Although adhesive to adjacent pericardium, parietal pleura, and lung, the mass did not invade these structures. The resected specimen measured 6.0 x 6.0 x 3.5 cm and consisted of a well-circumscribed, gray to tan mass, completely surrounded by a thin fibrous capsule. In cross-section the cystic component of the mass contained turbid, hemorrhagic fluid, and was multilocular. A polypoid nodule, 1.2 cm in greatest extent, projected into the cyst cavity (Fig 1). Light microscopic examination showed the cyst to be lined by stratified, nonkeratinizing squamous epithelium. In addition to the solid nodule, multifocal thickening was noted in the cyst wall, consisting of nests of tumor cells within fibrous tissue.
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Fig 1. Macroscopic appearance of the cut surface of our patient’s resected mass. The mass was well circumscribed, and a single 1.2-cm polypoid excrescence projected into the lumen of a cystic cavity.
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The tumor cells were basaloid in appearance, and an area of metaplastic-appearing squamous epithelium was seen in continuity with the basaloid cells. The tumor cell nuclei were uniform and oval in shape. The mitotic rate was 5 to 10 per high-power fields (HPF). No vascular or lymphatic invasion was seen (Figs 2, 3).
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Fig 2. Microscopic appearance of the resected specimen showing benign squamous epithelium in continuity with basaloid tumor cells (hematoxylin and eosin; original magnification x 50).
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Fig 3. Microscopic components of the resected specimen mainly included relatively uniform small cells. Mitotic figures were evident. The tumor cells were basaloid in appearance (hematoxylin and eosin; original magnification x 100).
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Immunohistochemically, the tumor cells demonstrated strong, diffuse reactivity for keratin and scattered reactivity for antiepithelial membrane antigen and Ber-EP4. The tumor cells did not stain for neuron-specific enolase, S-100 protein, synaptophysin, chromogranin, or Leu-7. The histological diagnosis was basaloid carcinoma of the thymus. The postoperative course was uneventful and the patient received 56 Gy of postoperative radiotherapy delivered as x-rays (10 MV) by a linear accelerator. The patient has survived with no recurrence 25 months postoperatively.
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Comment
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Since the specific histopathologic characteristics of basaloid carcinoma of the tongue, hypopharynx, and larynx first were described by Wani and colleagues in 1986 [1], similar tumors have been observed in various other locations, such as the skin, anal canal, and lung [2, 3]. However, basaloid carcinoma is rare among thymic carcinomas, with only 7 cases reported in English. The clinicopathologic features, treatment, and prognosis of these 7 cases and ours are summarized in Table 1. The patients ranged from 45 to 65 years (mean age, 58 years), and included 4 men and 4 women. The most common symptom was dyspnea referable to mass effect (38%). Four patients had no symptoms (50%). Five patients (62%) had an associated multiloculated thymic cyst (MTC). According to previous reports, a MTC is most often not associated with thymic carcinoma, but rather with prominent lymphoid infiltrates such as those seen in mediastinal Hodgkin’s lymphoma and seminoma [6]. Iezzoni and associates [7] have argued that basaloid carcinoma of the thymus may arise incidentally within a preexisting MTC.
All 7 previous patients underwent surgical resection. Pulmonary metastasis was detected in 2 patients, both with large masses (10 and 20 cm in diameter) (Cases 3 and 5). Follow-up results are available for only 4 patients, 2 of whom were alive 24 months postoperatively. Although data regarding the prognosis of this tumor are incomplete, the lesion is considered to show low-grade histology and is felt to have a favorable clinical course. However, the development of pulmonary metastases in 2 patients attests to some degree of metastatic potential. Frequency of mitosis is considered to be an indication of the biologic aggressiveness of a neoplasm. The mitotic rate in our case was 5 to 10 per HPF (mean, 8), while 3 of the earlier cases reportedly showed no mitotic figures (cases 1, 2, 4). Basaloid carcinomas of the thymus, then, do not have uniformly low-grade histology, and may have differing biologic potentials. The diagnosis has been made only by pathologic examination of surgical specimens, and therefore, resection is the diagnostic and therapeutic procedure required for this disease. When assessing a partially cystic anterior mediastinal mass by imaging studies, basaloid carcinoma of the thymus should be considered in the differentiate diagnosis. Furthermore, concurrence of this carcinoma with a MTC illustrates the importance of thorough pathologic examination of multilocular thymic masses, since 62% of the reported basaloid carcinomas were associated with a MTC. The effectiveness of chemotherapy and radiotherapy has not been determined for this tumor, again pointing to resection as the optimal management. Further long-term follow-up, and examination of additional cases is desireable to clarify the typical and potential behavior of this unusual tumor, as well as specific prognostic factors.
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References
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Wain S.L., Kier R., Vollmer R.T., Bossen E.H. Basaloid squamous carcinoma of the tongue, hypopharynx, and larynx. Hum Pathol 1986;17:1158-1166.[Medline]
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Kheir S., Hickey R.C., Martin R.G., Mackay B., Gallager H.S. Cloagenic carcinoma of the anal canal. Arch Surg 1972;104:407-415.[Abstract/Free Full Text]
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Snover D.C., Levine G.D., Rosai J. Thymic carcinoma. Five distinctive histological variants. Am J Surg Pathol 1982;6:451-470.[Medline]
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Hofmann W., Moller P., Manke H.G., Otto H.F. Thymoma. A clinicopathologic study of 98 cases with special reference to three unusual cases. Pathol Res Pract 1985;179:337-353.[Medline]
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Suster S., Rosai J. Multilocular thymic cyst. Am J Surg Pathol 1991;15:388-398.[Medline]
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Iezzoni J.C., Nass L.B. Thymic basaloid carcinoma. Mod Pathol 1996;9:21-25.[Medline]
Accepted for publication April 23, 1999.
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Abstract
Introduction
