Granular cell tumors: a report of six cases

Granular cell tumor is a soft tissue neoplasm that originates in the nervous system and arises at virtually any body site, but is mainly found in the skin, oral cavity or digestive tract [1‐3]. Most of them are benign and reportedly malignant cases are rare, occurring in only 1% or 2% of cases [4‐7]. We report on our findings in six patients who developed granular cell tumor in the mammary gland, esophagus, subcutaneous tissue and muscle.

Granular cell tumor was first reported by Abrikossoff [1] by the name of granular cell myoblastoma. One of its characteristics is that eosinophilic granules are contained in the cytoplasm of cells. Since the positive rates for S-100 protein and neuron specific enolase are high, currently it is thought that this tumor originates from Schwann cells. They account for an incidence of 0.5% among soft tissue tumors, and it has been reported that they primarily occur in or beneath the skin, or in the submucosa of the tongue, throat, chest wall, or bronchus. The tumor is commonly found in those aged 10 to 50 years old, and more often in women than in men [3, 8‐11]. Granular cell tumor of the breast is largely a disease affecting women, as it is with other breast malignancies, but has also been described in men, accounting for 6.6% of granular cell tumor of the breast [12].

About 2% of all granular cell tumor cases are malignant [4‐7]. A tumor 3 cm or less in size can be regarded as benign. However, if the tumor grows rapidly and forms an ulcer, malignancy should be suspected.

From a histopathologic perspective, Fanburg Smith and colleagues [5] proposed the following six criteria to determine whether a tumor is malignant or not: (1) the presence of necrosis, (2) the emergence of spindle cells, (3) a vacuolar nucleus with an enlarged nuclear body, (4) increase in nuclear division (2 mitoses/10HPF), (5) increase in the nucleoplasmic ratio, and (6) polymorphism. If none of these diagnostic criteria are met, the tumor is considered to be benign. If one or two criteria are met, the tumor is considered to be atypical, and if three or more criteria are met, the tumor is considered to be malignant.

Sonobe and colleagues [6] divided malignant granular cell tumors into two groups: those that are malignant both histologically and clinically, and those that are histologically benign but clinically malignant. The most common metastasis sites of malignant granular cell tumor are the lymph nodes, followed by the lungs. Insufficient tumor resection often results in local recurrence, and has a tendency to spread both lymphogenously and hematogenously. Reportedly, chemotherapy and radiotherapy treatments cannot be expected to be effective, with surgical resection being the primary option [4‐7]. Resection with adequate margins is necessary because the tumor has no capsule and is proliferation invasive. All tumors in our six cases were small in diameter, and benign histologically (Table 1).

In many cases, a granular cell tumor that has occurred in the breast is diagnosed to be invasive ductal carcinoma by imaging, and our patients with such a condition also showed spiculation on MMG images [13‐18]. The MMG and US appearances of granular cell tumor pose a diagnostic dilemma because of its similarity to breast malignancy.

A granular cell tumor that has developed in the submucosa of the esophagus is a non-pedunculated SMT with a smooth surface and pale yellow color, and both of our two cases presented the same characteristics [19‐22]. Granular cell is uncommon, mainly occurring on the skin, tongue and oral cavity as a single nodule. The disease in 30% to 45% of cases affects the skin, followed by the area of the head and neck, where the most frequent location is intraoral in the tongue and the soft and hard palate [11, 19‐24]. Other locations affected are the breast, the gastrointestinal tract, the respiratory tract, the thyroid gland, the urinary bladder, the central nervous system, and female genitalia. Location in the skeletal muscle region, as in our case, is rare. One of our patients was found with a granular cell tumor in the skeletal muscle [25].

In the gastrointestinal tract, the tumor often occurs in the esophagus and is rarely found in the large intestine [19‐22]. Granular cell tumor that has developed in the gastrointestinal tract must be differentiated from other submucosal tumors such as steatoma, smooth muscle tumor, neurogenic tumor and gastrointestinal stromal tumor. On endoscopic examination, the tumor is a very hard, smooth-surfaced submucosal tumor which appears as a yellow or yellowish-white hemispherical protrusion with a thin mucous membrane, and is sometimes called "molar tooth" or "sweet corn." It is rare that ulcerous lesions or recesses are observed on the mucosal surface [19‐22].

For differential diagnosis of a granular cell tumor in the subcutaneous tissue and muscle, candidates include: malignant fibrous histiocytoma, alveolar soft part sarcoma, desmoid, granulomatous, and nodular fasciitis [7, 23‐25]. Granular cell tumor of the breast arises from intralobular breast stroma and occurs within the distribution of the cutaneous branches of the supraclavicular nerve [17, 18]. When occurring in the breast, the tumor is often found in the upper inner quadrant unlike breast cancer that is found in the upper outer quadrant [17, 18]. Since the tumor affects the innervation of the skin, contractions or shrinkage of the skin sometimes occur. Traditional imaging techniques, including MMG and US scanning, are widely employed when investigating the presence mass. However, the issue with these modalities in cases of granular cell tumor is that the radiological findings are often indistinguishable from breast cancer. On MMG, the tumor is seen as a substantial round-shaped lesion with distinct edges of the hyperplasia invading into the surrounding tissues, and irregularity, speculation, isodensity sometimes associated with hypodense rims, and heterogenicity are commonly observed (Figure 1). Mass calcification was not observed in our cases. On the other hand, on US, the edges of the hyperplasia are not distinct and attenuation of posterior echo often occurs. Common features include solid, heterogeneous, poorly defined masses with high depth/width ratio (Figure 1). They are generally hypo-echoic and display posterior shadowing with a coarse internal echo and high boundary echo. For these reasons, it is necessary to perform differential diagnosis between breast cancer and invasive ductal carcinoma based on the images [13‐18]. The range of US findings are as broad as those of MMG, they are often suggestive of malignancy and most importantly there are no recognized features specific for granular cell tumor of the breast.

Granular cell tumor is a neoplasm that develops in the soft tissues, mainly in the skin, oral cavity and gastrointestinal tract, but the tumor is relatively rare. Granular cell tumor in all of our cases was benign, and no recurrence after resection has been found.

In accordance with the regulations of the Human Investigation Committee of the Tokyo Women’s Medical University, written informed consent was obtained from the patient for publication of this report and any accompanying images.

No extramural funding was used for this study.