Testicular fibrothecoma: a morphologic and immunohistochemical study of 16 cases

Benign intratesticular spindle cell lesions are rare. Herein, we report the morphology, immunohistochemical characteristics, and prognosis of 16 cases of testicular fibrothecoma. The mean age at diagnosis was 44 years (16 to 69 y). Of 15 patients with information, 14 presented with a palpable testicular mass and 1 with heaviness in the scrotum. Medical histories included bilateral orchidopexy as a child (n=1) and testicular atrophy receiving testosterone replacement (n=1). The average size was 1.8 cm (median 2 cm; range, 0.5 to 7.6 cm). All cases were intratesticular, although 13 were abutting the tunica albuginea with others centered on the rete testis (n=2), or were indeterminate on biopsy (n=1). Eleven cases were relatively well circumscribed, although not encapsulated, with 1 being infiltrative and 4 not evaluable. Four tumors showed entrapment of seminiferous tubules. Half of the fibrothecomas showed a mixed storiform pattern and short fascicles, with 6 storiform only and 2 short fascicles only. One half of the tumors were very hypercellular. Cases were equally split between having plumper ovoid as opposed to spindled pointed nuclei, with all cases lacking prominent nucleoli. Eleven cases had 0 to 2 mitoses per 10 HPF, 3 had 4 to 5 mitoses per 10 HPF, and 2 had 9 to 10 mitoses per 10 HPF. Collagen deposition either in bands or investing single cells ranged from none to extensive, with 10/16 cases having at least a moderate amount. Immunohistochemical positivity was as follows: inhibin (11/13, patchy to diffuse); calretinin (5/9); Melan-A (4/4); pan keratin (5/8); BCL2 (3/4); CD34 (3/8); S100 (4/8); muscle-specific actin (4/4); and desmin (5/8). Patients were followed up for a mean of 71.8 months (range, 3 to 144 mo). All were well with no evidence of disease. Of the 2 men with 9 to 10 mitoses per 10 HPF, 1 died of other causes 5 years and 8 months later, and the other had no evidence of disease at 4 years and 10 months after surgery. In summary, testicular fibrothecomas are rare with somewhat variable histology and can have worrisome histologic features such as minimal invasion into surrounding testis, high cellularity, and increased mitotic rate. Their immunoprofile is variable and typically not diagnostic. Despite some worrisome histologic features, they appear uniformly benign in their behavior.