Discussion

Granular cell tumors in the breast are rare, typically benign, and can often mimic malignant lesions both clinically and radiologically. They present a diagnostic challenge because they may exhibit features similar to breast carcinomas, such as irregular margins and heterogeneous echo patterns on ultrasound. Studies suggest that the incidence of these tumors in the breast is low, accounting for approximately 5%-8% of all GCTs.¹

Granular cell tumors typically present as firm, usually non-tender masses and may be found incidentally on routine mammograms or during physical examinations. They can vary in size and are often mobile unless they are located deep and adherent to the chest wall or overlying fascia, where they may feel fixed.¹

GCTs may grow slowly without significant change over time. Any rapid change in size or newly associated symptoms should prompt further investigation to rule out malignant transformation or other complicating factors. Importantly, GCTs can occasionally be associated with pain or discomfort if they impinge on nerves or have a deep location affecting muscle or connective tissue layers.^{2, 3} They do not usually present with systemic symptoms unless they are part of a rare malignant variant. However, patients with GCTs can present with skin changes such as thickening or dimpling over the tumor, which can further complicate the clinical picture, suggesting more aggressive underlying pathology.¹

Mammographically, GCTs usually present as high-density masses with irregular or spiculated margins. These characteristics overlap significantly with those of invasive breast carcinomas, making it difficult to differentiate between the two based solely on mammographic findings.¹ Occasionally, GCTs may appear as circumscribed oval masses, mimicking benign conditions such as fibroadenomas.¹

On ultrasound, GCTs are typically hypoechoic masses with indistinct or spiculated margins and may exhibit posterior acoustic shadowing as in malignancies, thus necessitating needle biopsy to achieve a definitive diagnosis.³

While not always utilized, MRI can provide additional detail, particularly in complex cases. GCTs on MRI generally appear as well-defined masses with low signal intensity on T1-weighted images and variable signal intensity on T2-weighted images. They may enhance uniformly or heterogeneously after contrast administration.¹

These details emphasize the importance of a comprehensive diagnostic approach, including imaging and biopsy, to distinguish GCTs from more aggressive breast lesions.

Granular cell tumors arise from Schwann cells and are histologically defined by polygonal cells with granular eosinophilic cytoplasm, arranged in clusters or sheets. The cytoplasmic granules, indicative of lysosomal origin, are PAS-positive and diastase-resistant. Immunohistochemically, GCTs are consistently positive for neural markers and negative for epithelial and melanocyte markers, helping to distinguish them from other neoplasms.

Most GCTs are benign, but the risk of recurrence or rare malignant transformation makes thorough surgical management essential.¹ The standard treatment is wide local excision with clear margins to prevent recurrence, which can range from 2%-8%.^{2, 3} Clear margins and meticulous surgical techniques are crucial for minimizing recurrence. In rare cases of malignant GCTs, management may require additional therapies similar to those used for breast cancers, highlighting the importance of precise pathological assessment and follow-up.³