Prostatic leiomyoma with atypia: follow-up study of 10 cases

Abstract

We studied the clinical and histologic features of 10 cases of prostatic leiomyoma with atypical bizarre nuclei. Immunohistochemical studies were undertaken in 6 cases. Patient follow-up was obtained in all cases. Patients ranged in age from 50 to 82 years (mean, 65 years) and presented with urinary obstructive symptoms in 7 cases, abnormal digital rectal examination in 3 cases. The histologic findings consisted of a solid circumscribed expansile stromal nodule with abundant smooth muscle and variable numbers of atypical bizarre giant cells. The cells of the tumor displayed intense immunoreactivity for desmin, actin, and androgen receptor and weak to moderate reactivity for vimentin. Four local recurrences were seen, with a follow-up for 3 to 16 years (mean, 7.4 years), but no evidence of sarcomatous transformation occurred. Despite worrisome histologic appearance, a benign clinical behavior was seen in all cases.

Introduction

Leiomyoma of the prostate is a rare neoplasm; previous reports of this neoplasm consisted of single-case studies or a small series [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23]. Atypical leiomyoma of the prostate is extremely rare; only a few cases are reported [24], [25], [26], [27]. Prostatic leiomyoma with atypia, which is an extremely rare lesion, also has been referred to by a variety of terms, including atypical stromal hyperplasia, stromal hyperplasia with bizarre nuclei, symplastic leiomyoma, pseudosarcomatous lesion, and pseudoneoplastic lesion of the prostate gland [28], [29], [30], [31], [32], [33], [34].

The nuclear abnormalities in this lesion are identical to those of symplastic leiomyoma of the myometrium, raising concern for sarcoma. The etiology, diagnostic criteria, and clinical significance of this lesion are not well established, and features that separate this lesion from sarcoma are not defined. Previously, we reported 7 cases of this unusual soft tissue tumor of the prostate, with a mean follow-up of 2.9 years, as prostatic stromal hyperplasia with atypia (PSHA) with leiomyoma-like pattern [34]. The histologic and immunohistochemical findings in these cases were distinctively different from PSHA (see Discussion section), and we recognized that prostatic leiomyoma with atypical cells is a better terminology for this tumor. This study also expands our series to 10 cases, including the previously described 7 cases with an extended follow-up of 7.4 years, and underscores the apparent benign nature of this tumor.