Granular cell tumor of the penis: clinicopathologic evaluation of 9 cases

The occurrence of granular cell tumor (GCT) in penile tissue is very rare, with only 9 examples reported to date in the English-language literature. Herein, we describe the clinicopathologic and immunohistochemical findings in 9 additional cases. The patients ranged in age from 20 to 60 years (mean, 42 years; median, 40 years) at time of diagnosis. All penile tumors were solitary and arose in the dermis of the penile shaft (n=4), prepuce (n=3), and corona (n=2). A patient had a history of multiple cutaneous GCTs. Duration of symptoms before surgery ranged from 5 days to 2 years with the presence of an asymptomatic nodule representing the most common tumor-related complaint (n=8). The lesions ranged in size from 0.6 to 2.5 cm (mean, 1.5 cm; median, 1.5 cm). Microscopically, the tumors were moderate to highly cellular and were composed of oval to polygonal-shaped cells with abundant coarsely granular eosinophilic cytoplasm. Tumor cells grew in infiltrating nests, cords, and trabeculae and showed neural (n=2) and vessel wall (n=1) invasion or formed a relatively well-marginated solid nodule. Bland cytological features with only rare cells showing nucleomegaly (n=7) or spindling (n=3) were exhibited by 8 tumors. A tumor demonstrated diffuse nuclear atypia and was classified as "atypical." Mitotic activity ranged from 0 to 8 mitoses (mean, 1.4 mitoses) per 50 high-powered fields with no atypical division figures identified. All tumors tested showed moderate to strong immunohistochemical expression of S100 protein (n=6) and low-affinity nerve growth factor receptor (n=5), which was useful for detecting small deposits of tumor and helpful in evaluating surgical margins. Focal tumor cell immunoreactivity was observed for calretinin (4/6 cases) and glial fibrillary acidic protein (1/6 cases). All patients underwent simple (local) excision of their tumor. Complete follow-up data (mean, 21 years; interval range, 0.5-28 years) were available for 6 patients. No patient experienced recurrence or metastatic spread of tumor although surgical margins were microscopically involved by tumor in 5 cases. Benign GCT involving superficial soft tissue of the penis can be adequately managed by a simple excision. Patients with microscopically involved surgical margins can be clinically followed without immediate additional surgery.