Yonago Acta medica 2010;53:65–69

Tubular-Trabecular Type Basal Cell Adenoma ofthe Parotid Gland: A Patient Report
Motoki Nakabayashi*†, Kohei Shomori*, Shuichi Kiya‡, Tatsushi Shiomi*, Kanae
Nosaka* and Hisao Ito*
*Division of Organ Pathology, Department of Microbiology and Pathology, Tottori University Faculty of Medicine, Yonago 683-8503, †Division of Oral and Maxillofacial Biopathological Surgery, Department of Medicine of Sensory and Motor Organs, Tottori University Faculty of Medicine, Yonago
683-8504 and ‡Clinic of Otorhinolaryngology, Sanin-Rosai Hospital, Yonago 683-8605, JapanBasal cell adenoma (BCA) is an uncommon benign salivary gland neoplasm that includes
isomorphic basaloid cells. We report on a female patient with BCA that developed in theright parotid gland in her 50s. The present patient demonstrated a few tumor nests inthe fibrous capsule, and her tumor was larger than usual. These facts made us suspect ofmalignancy. Histopathologically, the tumor was characterized by multiple duct-like structures and tubular-trabecular masses composed of small isomorphic cells with hyperchromatic, round nuclei and an eosinophilic cytoplasm. It was difficult to determine whether
the ductal structures noted in the tumor capsule were invasive. By immunohistochemistry,tumor cells of the tubular nests were positive for cytokeratin 7 and that the outer cells of
tubular nests were positive for alpha smooth muscle actin ( SMA) and calponin. Tumor
cells were immuno-negative for S-100 protein and glial fibrillary acidic protein. The Ki-67
labeling scores of the cells were extremely low (< 1%). We could achieve an accurate diagnosis of BCA by immunohistochemistry with MIB-1 and other markers.
Key words: basal cell adenoma; immunohistochemistry; parotid gland
Salivary gland tumors are uncommon and constitute 2.0% to 6.5% of all head and neck tumors(Leegaard and Lindeman, 1969; van der Wal et al.,1992). Salivary gland tumors are histologicallydiverse and include various types and subtypes.
Therefore, the accurate diagnosis of salivary glandtumors is difficult in some patients. The majorityof salivary gland tumors are located in the parotid
gland (Satko et al., 2000; Ito et al., 2005; Gnepp,2009), and benign tumors predominate over malignant tumors (Satko et al., 2000). Pleomorphic
adenoma is the most common salivary gland tumor with an incidence ranging from 60% to 65%(Evenson and Cawson, 1985; Barnes et al., 2005;
Gnepp, 2009). On the other hand, basal cell ad-enoma (BCA) accounts for only 1% to 3% of allsalivary gland tumors and demonstrates a female
predominance of 2:1 (Luna and Mackay, 1976;
Satko et al., 2000; Vargas et al., 2002; Barnes etal., 2005; Gnepp, 2009). BCA was recognized as adistinct disease entity in 1991 by the World HealthOrganization (Seifert and Sobin, 1991). BCA tumors have been histopathologically classified into
solid (monomorphic), trabecular, tubular and membranous types (Ellis and Auclair, 1996). However,basal cells are found in various primary salivary
gland tumors either as a component of the tumor
or as pure basal cell neoplasms. In this regard, thedistinction between true BCA and other primarytumors mimicking the basal cell features of theAbbreviations: BCA, basal cell adenoma; CK, cytokeratin; GFAP, glial fibrillary acidic protein; SMA, alpha smooth muscle actin

65M. Nakabayashi et al.

salivary gland sometimes causes diagnostic difficulties (Seifert, 1996).
Here, we report on a female patient with BCA
occurring in the parotid gland in her 50s. Immunohistochemistry provided useful information thatallowed an accurate pathological diagnosis to beachieved in this patient.

Patient ReportaClinical summary
A Japanese woman in her 50s was admitted to theClinic of Otorhinolaryngology at San-in Rosai Hospital in 2009 due to a painless swelling in her rightparotid gland. A physical examination revealed a
hard-circumscribed nodule of 4 cm in diameter.
The lesion was first noticed in 2001 and had gradually enlarged without pain. Computed tomography
showed a round, well-circumscribed heterogeneousmass measuring 3.6 × 4.3 cm in the right parotid
gland. No calcification or cystic component wasseen in the tumor. Neck magnetic resonance imaging also revealed a heterogeneous, well-demarcatedmass in the right parotid gland. On a T1-weighted
image, the tumor was heterogeneously isointense tomuscle (Fig. 1a). On a T2-weighted image, the tumor demonstrated a heterogeneous moderate intensity. The signal intensity of the tumor on the T2weighted image was higher than that of the muscle(Fig. 1b).
Initially, her disease was clinically suspected
as pleomorphic adenoma. However, the probabilityof malignancy could not be ruled out so the patientunderwent surgery. There has been no recurrence
for 7 months after surgery.

bFig. 1. Contrast-enhanced magnetic resonance scans
showing homogeneous moderate enhancement of themass (arrow). Capsule-like enhancement is seen. a: T1weighed image. b: T2-weighed image.

and an eosinophilic cytoplasm (Figs. 2a and b).
There was no cartilage formation, mucous stroma
or necrosis in the tumor. The tubular portion of thetumor demonstrated a two-layered ductal structure.
Mitotic figures were extremely rare (× 400/highpower field). Nuclear atypia and mitotic figures
were not prominent. In some sections, there weretumor cells in the wall of the capsule (Fig. 2c).
An immunohistochemical examination
showed that the inner cells of the tubular components were positive for cytokeratin (CK) 7 andnegative for alpha smooth muscle actin ( SMA)
and calponin (Figs. 3a and b). On the contrary, theouter cells were negative for CK7 and positive for
SMA and calponin. Tumor cells were immuno-Pathological findings
Histopathologic examination revealed that the tumor, which was encapsulated with fibrous tissue,
was characterized by multiple duct-like structures
or solid and trabecular masses composed of small
isomorphic cells with hyperchromatic, round nuclei
66

Basal cell adenoma of the parotid gland

aabb
Fig. 3. Immunohistochemistry of the basal cell adenoma.
a: The tumor cells show immunoreactivity for cytokeratin 7. Bar = 50 μm.
b: Alpha smooth muscle actin immunoreactivity is noted in the outermost layer of the tubular type tumorcells. Bar = 50 μm.

negative for S-100 protein and glial fibrillary acidic
protein (GFAP). The stromal cells showed immunoreactivity for SMA, but not for S-100 protein or
glial fibrillary acidic protein. In addition, the frequency of Ki-67 positive tumor cells was extremely
low, being less than 1%. From these findings, thetumor was diagnosed as a tubular-trabecular BCA.

cFig. 2. Histopathology of the basal cell adenoma (hematoxylin and eosin stain).
a: The tumor cells demonstrate a tubular structure.
Bar = 50 μm.
b: Trabecular tumor cells and tumor cell nest formation. Bar = 50 μm.
c: Trabecular tumor cell nests are noted in the fibrouscapsule of the tumor, mimicking infiltration. Bar =100 μm.

Discussion
BCA is a rare, benign epithelial neoplasm of thesalivary gland. According to the literature, malig67

M. Nakabayashi et al.

nant transformation occurs in 4.3% of BCA (Nagaoet al., 1997). BCA frequently occurs in people ofover 50 years of age as a unilateral tumor with awell-circumscribed round or oval appearance. Apainless, slowly enlarging mass is the most common clinical symptom (Nagao et al., 1982; Jang etal., 2004). BCA tumors are usually smaller than 3cm. In the present patient, the site of occurrence,
past history, age and sex were compatible withthose written in previous reports, but the tumor size
was not compatible. Microscopically, the tumor
was histopathologically classified as BCA of thetubular-trabecular type.
The cellular type of pleomorphic adenoma isdifficult to distinguish from BCA; however, myxoid or cartilage formation characteristic of pleomorphic adenoma was not observed in the present
patient (Ellis and Auclair, 1996; Minicucci et al.,2008). In addition, immunohistochemical stainingof the tumor cells was negative for S-100 protein
and GFAP. Previous reports have shown that theouter tumor cells in pleomorphic adenoma exhibita very heterogeneous distribution or the simultaneous presence of S-100 protein and GFAP (Mori etal., 1990; Ogawa et al., 1990; Shida et al., 2005).
Basal cell adenocarcinoma shares common
clinical and histological similarities with BCA(Klijanienko et al., 1999; Machado de Sousa etal., 2001). Cytology differences, infiltration andperineural invasion help distinguish basal cell adenocarcinoma from BCA. The present patient demonstrated a few tumor nests or glands in the fibrouscapsule. However, nuclear atypia and mitotic figures were not prominent. Moreover, no necrosis orhemorrhaging was observed. We considered thattumor cells in the capsule were not of the invasive
origin but a part or component of fibrous tissues.
It is difficult to differentiate between BCA
with a two-layered tubular structure and the tubular
type of adenoid cystic carcinoma because atypicaltumor cells are relatively scarce in both types oftumor. The Ki-67 labeling index is a useful markerof cell proliferation (Murakami et al., 1992; Nagaoet al., 1998). The Ki-67 labeling indices of adenoid
cystic carcinoma have been reported to range from

13.6% to 34.7%. On the other hand, we found aKi-67 labeling index of less than 1% in the presentpatient.
We present a patient with BCA classified as arare benign tumor that was difficult to differentiate from other tumors with a two-layered structure.
We emphasize the importance of immunohistochemistry for obtaining an accurate diagnosis ofBCA, particularly because BCA has the potential
to be malignant.
Acknowledgments: We thank Mr. Norihisa Itaki and Ms.
Chie Yamazaki for their technical support.
References
1 Barnes L, Eveson JW, Reichart P, Sidransky D. World
Health Organization classification of tumours. Pathology and genetics of head and neck tumours. Lyon: International Agency for Research on Cancer Press; 2005.
p. 261–262.
2 Dardick I, Daley TD, van Nostrand AW. Basal cell adenoma with myoepithelial cell-derived “stroma”: a newmajor salivary gland tumor entity. Head Neck Surg
1986;8:257–267.
3 Ellis GL, Auclair PL. Tumor of the salivary glands. Atlas of tumor pathology. Washington DC: Armed Forces
Institute of Pathology; 1996. p. 90–94.
4 Evenson JW, Cawson RA. Tumours of the minor(oropharyngeal) salivary glands: a demographic studyof 336 cases. J Oral Pathol 1985;14:500–509.
5 Gnepp DR. Diagnostic surgical pathology of the headand neck. London: W. B. Saunders; 2009. p. 351–365.
6 Ito FA, Ito K, Vargas PA, de Almeida OP, Lopes MA.
Salivary gland tumors in a Brazilian population: aretrospective study of 496 cases. Int J Oral Maxillofac
Surg 2005;34:533–536.
7 Jang M, Park D, Lee SR, Hahm CK, Kim Y, Kim Y, etal. Basal cell adenoma in the parotid gland: CT and MRfindings. AJNR Am J Neuroradiol 2004;25:631–635.
8 Klijanienko J, el-Neggar AK, Vielh P. Comparative cytologic and histologic study of fifteen salivary basal-celltumors: differential diagnostic considerations. DiagnCytopathol 1999;21:30–34.
9 Leegaard T, Lindeman H. Salivary-gland tumors.
Clinical picture and treatment. Acta Otolaryngol Suppl
1969;263:155–159.
10 Luna MA, Mackay B. Basal cell adenoma of the parotid gland. Case report with ultrastructural observations.
Cancer 1976;37:1615–1621.
11 Machado de Sousa SO, Soares de Araujo N, Correa
L, Pires Soubhia AM, Cavalcanti de Araujo V. Im-68

Basal cell adenoma of the parotid glandmunohistochemical aspects of basal cells adenoma andcanalicular adenoma of salivary glands. Oral Oncol
2001;37:365–368.
12 Minicucci EM, de Campos EB, Weber SA, Domingues
MA, Ribeiro DA. Basal cell adenoma of the upper lip from minor salivary gland origin. Eur J Dent
2008;2:213–216.
13 Mori M, Yamada K, Tanaka T, Okada Y. Multiple
expression of keratins, vimentin, and S-100 protein in
pleomorphic salivary adenomas. Virchows Arch B CellPathol Incl Mol Pathol 1990;58:435–444.
14 Murakami M, Ohtani I, Hojo H, Wakasa H. Immunohistochemical evaluation with Ki-67: an application tosalivary gland tumors. J Laryngol Otol 1992;106:35–38.
15 Nagao K, Matsuzaki O, Saiga H, Sugano I, Shigematsu
H, Kaneko T, et al. Histopathologic studies of basal celladenoma of the parotid gland. Cancer 1982;50:736–745.
16 Nagao T, Sugano I, Ishida Y, Matsuzaki O, Konno A,Kondo Y, et al. Carcinoma in basal cell adenoma of theparotid gland. Pathol Res Pract 1997;193:171–178.
17 Nagao T, Sugano I, Ishida Y, Hasegawa M, MatsuzakiO, Konno A, et al. Basal cell adenocarcinoma of thesalivary glands: comparison with basal cell adenoma
through assessment of cell proliferation, apoptosis, andexpression of p53 and bcl-2. Cancer 1998;82:439–447.
18 Ogawa I, Nikai H, Takata T, Miyauchi M, Ito H, Ijuhin N.
The cellular composition of basal cell adenoma of theparotid gland: an immunohistochemical analysis. Oral

Surg Oral Med Oral Pathol 1990;70:619–626.
19 Satko I, Stanko P, Longauerova I. Salivary gland tumors in the stomatological clinics in Bratislava. J Craniomaxillofac Surg 2000; 28:56-61.
20 Seifert G, Sobin LH. Histological typing of salivary
gland tumors. World Health Organization International
Histological Classificationof Tumors. 2nd ed. Berlin:Springer-Verlag; 1991. p. 20–21.
21 Seifert G. Classification and differential diagnosisof clear and basal cell tumors of the salivary glands.
Semin Diagn Pathol 1996;13:95–103.
22 Shida H, Tanaka A, Fukuda M, Shigematsu H, Kusama
K, Sakashita H. [A case of basal cell adenoma in theparotid gland.] Nippon Kokugeka Gakkai Zasshi
2005;51:352–355 (in Japanese with English abstract).
23 van der Wal JE, Snow GB, van der Wal I. Histologicalreclassification of 101 intraoral salivary gland tumours(new WHO classification). J Clin Pathol 1992;45:834–835.
24 Vargas PA, Gerhard R, Araujo Filho VJ, de Castro IV.
Salivary gland tumors in a Brazilian population: a retrospective study of 124 cases. Rev Hosp Clin Fac Med
Sao Paulo 2002;57:271–276.
Received July 6, 2010; accepted, July 23, 2010
Corresponding author: Kohei Shomori, MD69