Schwannoma of the Breast: Presentation of Four Cases and Review of the Literature

Abstract

Background: Schwannoma is a usually a benign tumor of nerve sheath origin, most frequently occurring in the neck, the head, and the extremities. Its occurrence in breast tissue is rare. There have been only 29 proven cases of breast schwannoma described in the literature. Cases: We describe the clinicopathologic presentation, imagery findings, and management of four cases of breast schwannoma treated with surgery and review those documented in the literature. All patients in this series are doing well without any evidence of recurrent disease. Conclusion: Breast schwannomas are usually well circumscribed, noninvasive, and show a benign appearance on imagery. Complete surgical excision is the best choice of treatment. (J GYNECOL SURG 28:385)

Introduction

Schwannoma is usually a benign and slow-growing tumor of nerve sheath origin. It can be observed anywhere in the body, but the most common locations are the neck, the head, and the flexors surfaces of the extremities.¹ Most primary tumors of the breast have an epithelial origin; therefore it is extremely rare for schwannoma to occur in breast tissue.² Twenty-nine previous case reports were identified in the literature since 1973. We report the largest case series of four cases of benign solitary schwannoma presenting as a breast lump and discuss the mammographic and ultrasonographic findings and the management of such tumors.

Cases

Case 1

A 37-year-old woman with no significant past medical history presented with a painless lump in the upper-outer quadrant of the right breast, which had been noticeable for 7 months and had progressively increased in size. Physical examination revealed a 40-mm, well-circumscribed, painless, mobile, and firm mass, with no evidence of axillary lymphodenopathy. Mammography showed a 35-mm, circumscribed, and hypodense mass without microcalcification. This lesion was classified as ACR 3 (American College of Radiology). On ultrasonography, the lesion was well circumscribed, parallel in orientation, hypoechoic, and solid with moderate acoustic enhancement. No enlarged axillary lymph nodes were noted. Although the mammography and ultrasonography findings indicated that the mass was benign, the patient chose to have the tumor excised rather than conservative follow-up. Macroscopically, the tumor measured 36 mm and was encapsulated, firm, homogenous, and whitish on section. Histological examination revealed spindle cells, often arranged in a palisading fashion or in an organoid arrangement. No atypical mitotic figures were present. The tumor was diffusely immunoreactive for S-100 protein and negative for desmin, cytokeratin, and CD34. Based on these findings, a histopathological diagnosis of schwannoma of the breast was made. At 5 years of regular follow-up, the patient did not show any evidence of recurrent disease.

Case 2

A 31-year-old female with no significant past medical history complained of a mass that had been growing slowly in her left breast for more than 3 years. Clinical examination revealed a 50-mm, well-circumscribed, and firm mass at the union of external quadrants. There were no signs of nipple discharge, skin changes, or regional lymphadenopathy. Mammography showed a well-defined and dense nodule without microcalcification, visible only on the angled side view. Supplementary ultrasonography showed a 45-mm, hypoechoic, heterogeneous, and well-defined mass, which corresponded to the mammographic abnormality and the clinically palpable lump. These findings suggested a benign lesion. Options of ultrasound-guided core needle biopsy and surgical excision were discussed, and the patient subsequently had a surgical excision, and a 42-mm, well-defined mass was removed. The cut surface was homogenous and the specimen was yellowish white. Hematoxylin-eosin staining showed fascicles of fusiform cells with elongate nuclei and indistinct cytoplasmic borders, which were often arranged in a palisading pattern. The tumor was diffusely immunoreactive for S-100 protein and negative for desmine, CD34, and cytokeratine. There were no atypical cells, and no mitosis was observed. Based on these findings, a histopathological diagnosis of schwannoma of the breast was made. At 3 years of regular follow-up, the patient did not show any evidence of recurrent disease.

Case 3

A 29-year-old asymptomatic female with a past medical history of bilateral breast adenofibroma treated with surgery 3 years ago presented with a palpable lump in her left breast. She first noted it 2 weeks prior on self-examination. She had no family history of breast carcinoma. Clinical examination revealed a 30-mm, well-defined, firm, and mobile lump in the left lower outer quadrant. No mass was detected on mammography but sonography revealed a 25-mm, well-defined, hypoechoic, and deep located mass with homogenous internal echo within the breast. Subsequently, the patient had a surgical excision. A well-encapsulated firm mass was removed, and it measured 25 mm and was yellowish white on cross-section. Histological examination revealed a benign mesenchymatous proliferation: spindle-shaped cells with poorly defined eosinophilic cytoplasm and pointed basophilic nuclei, set in a variably collagenous stroma (Antoni A tissue). Areas of cells with parallel arrays of nuclear palisading known as Verocay bodies were noted on high power. On immunohistochemical staining, the tumor cells were positive for vimentine and S-100 protein, consistent with a diagnosis of schwannoma. At 2 years follow-up, the patient was doing well with no recurrence.

Case 4

A 32-year-old woman presented with a 1-month history of a left breast mass. A physical examination revealed a 15-mm, well-limited, elastic-soft, smooth, and mobile mass in the upper left breast. There was no evidence of axillary lymphadenopathy. On screening mammogram, the lesion appeared as a circumscribed, round-oval, and equally dense nodule without microcalcifications. Ultrasonography revealed a 20-mm, oval-shaped, hypoechoic, and heterogeneous mass with moderate acoustic enhancement (Fig. 1). The tumor was hypocascular on color Doppler with a 10-mm inflammatory enlarged axillary lymph node. Although, these findings suggest that the mass was benign, a surgical excision was performed under local anesthesia. Macroscopically, the mass was well defined and oval-shaped, measuring 20 mm, and was entirely covered by a thin, whitish capsule. A microscopic examination revealed a structure of interlacing bundles of numerous elongated spindle-shaped cells, arranged in a palisading pattern with occasional Verocay bodies (Fig. 2). No atypical mitotic figures were present. Immunohistochemically, the tumor cells exhibited intense staining for S-100 protein (Fig. 3). These findings were compatible with schwannoma. At 2 years of regular follow-up, the patient was doing well with no evidence of recurrent disease.

FIG. 1.

Ultrasonography showed a well-circumscribed heterogeneous and hypoechoic mass.

FIG. 2.

Areas of spindle-shaped cells with parallel arrays of nuclear palisading known as Verocay bodies.

FIG. 3.

S-100 protein staining was positive in the tumor cell cytoplasm.

All patients in this case series were still alive at the time of preparing this report and did not show any evidence of recurrent disease at their regular follow-up.

Discussion

Schwannoma is a benign and slow-growing tumor that usually arises on peripheral nerves or spinal roots.^1,2 Neurilemoma, neurinoma, and schwannoma are considered to be synonymous. Any part of the body can be affected, but the most common locations include the head, neck, and extensor surfaces of the extremities.³ However, the localization in the breast is very unusual and accounts for only 2.6% of schwannomas according to Das Gupta et al.⁴ To the best of our knowledge, only 29 previous cases have been reported in the literature. The clinical features of the all cases, including those of our case, are reported in Table 1.^1–3,5–23 Twenty-seven patients were female and six were male, and the patients ranged in age from 18 to 83 years, with a mean age of 45.9 years. The tumors were most often located in the upper outer quadrant following by the upper inner quadrant. The tumor size ranged from 0.7 to 11 cm with a mean size of 3.5 cm.

Table 1.

Previously Reported Cases of Breast Schwannomas

Author	Year	Age	Sex	Side	Q	Size (cm)
Collins⁵	1973	43	F	R	UO	2.0
Majmudar⁶	1976	18	F	R	LI	2.5
Walt⁷	1982	38	F	L	UO	3.0
	1982	39	F	R	UO	0.8
Krishnan⁸	1982	43	F	R	UO	3.0
Harrison⁹	1989	24	F	L	UI	6.0
Cohen¹⁰	1991	80	F	R	Lo	9.0
	1991	75	M	NS	NS	9.0
	1991	20	F	NS	NS	2.8
	1991	NS	F	NS	NS	1.0
Martinez-Onsurbe¹¹	1992	83	M	L	UO	4.0
Bernadello¹²	1994	18	F	R	UI	1.0
Hauser¹³	1995	27	F	R	UI	1.2
Mondal¹⁴	1996	38	M	R	O	3.5
	1996	56	M	R	O	8.6
	1996	74	M	R	Lo	11.0
Gultekin¹⁵	1996	50	F	L	UI	0.7
Tokita¹⁶	1996	62	F	R	UO	1.5
Galant¹⁷	1997	25	F	R	AT	3.0; 1.6
Cho¹⁸	2001	76	F	R	LO	NS
Gupta¹⁹	2001	35	M	L	UI	2.0
	2001	56	F	R	O	3.0
Tohnosu²⁰	2002	64	F	R	UO	2.3
Rashidi²¹	2005	27	F	R	LO	7.0
Uchida²	2005	45	F	L	C	3.1
Lee²²	2006	41	F	R	NS	NS
Bellezza¹	2007	58	F	R	UO	4.4
Balci²³	2009	61	F	L	UO	1.2
Dialani³	2011	64	F	L	UO	1.0
Present cases	2012	37	F	R	UO	3.6
	2012	31	F	L	O	4.2
	2012	29	F	L	LO	2.5
	2012	32	F	L	U	2.0

Q=quadrant involved; F=female; M=male; R=right; L=left; U=upper; Lo=lower; UO=upper outer; LI=lower inner; UI=upper inner; O=outer; AT=axillary tail; C=central; NS=not specified.

Mammographic and ultrasound findings in schwannoma of the breast have not been widely described due to the rarity of this entity. Mammographically, schwannomas are most commonly described as a nonspecific, well-defined, round or oval, and equally dense nodule.^{1–3,12,16,18,23} Also, a normal mammogram without any detectable mass,^17,20 and an ill-defined area of dense soft tissue¹⁵ have been reported. In our cases, the mammographic findings were similar to those reported previously. In fact, in one patient, the mammography was normal, and in the other three patients, the lesion appeared as a circumscribed, round-oval, and dense nodule without microcalcifications. On ultrasonography, more variation in appearance has been reported. However, it is most commonly reported as a solid hypoechoic, well-defined mass of benign appearance with variable posterior acoustic enhancement.^{1,3,12,16–18,20,23} Also, a cystic degeneration has been reported.² For these reasons and based solely on imagery, it can be very difficult to distinguish schwannoma in the breast from other benign or malignant tumors.

Microscopically, classic schwannoma is an encapsulated neoplasm and consists of two alternating components in variable proportions known as Antoni A tissue and B tissue. Antoni A tissue is an organized cellular component and consists of monomorphic spindle-shaped Schwann cells, with poorly defined eosinophilic cytoplasm and pointed basophilic nuclei, set in a variable collagenous stroma.² These cells commonly form a palisading arrangement known as Verocay bodies. Antoni B is a relatively less cellular component and contains more loosely arranged cells.^24,25

Given the histological characteristics of breast schwannoma, the differential diagnosis from other lesions showing spindle cells may be difficult and includes phylloides tumor, fibroadenoma with minor epithelial components, fibromatosis, neurofibroma, myoepithelioma, myofibroblastoma, and metaplastic carcinoma.^1,2 However, immunohistochemically, schwannoma cells exhibit intense and uniform staining for S-100 protein,²¹ which helps to establish an accurate diagnosis.

A cytological diagnosis of schwannoma of the breast may be possible by fine-needle aspiration cytology.^1,2 However, schwannoma of the breast is such an infrequently encountered tumor that fine-needle aspiration cytology may not result in a correct diagnosis in some cases,² and in such cases a surgical excision is recommended. Primary malignant schwannomas of the breast have also been reported,^26–29 and these tumors showed a benign appearance on imagery, and fine-needle aspiration cytology revealed atypical mesenchymal cells.^27,28 Due to the rarity of breast schwannoma, the large differential diagnosis, and the possibility of underestimating a malignant entity, all our patients underwent a surgical excision rather than a fine-needle aspiration.

Adequate treatment of solitary benign schwannoma consists of simple enucleation of the encapsulated tumor. To date, recurrence after surgical excision has not been reported.

Conclusion

We have presented four cases of schwannoma of the breast and reviewed the literature. These tumors are usually well circumscribed, noninvasive, and usually show a benign appearance on imagery. A complete surgical excision of this lesion helps in making the definitive diagnosis, and represents the best choice of treatment.

Footnotes

Disclosure Statement

No competing financial interests exist.

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