Most common prostate tumor in the first 2 decades of life (ave. 7 years); very rare in adults.
Presents with obstructive urinary symptoms.
Gross: fleshy tumor with history of rapid growth.
May initially present as a polypoid mass in prostatic urethra and can mimic a fibroepithelial polyp.
Most commonly embryonal type, alveolar type less common.
Embryonal RMS shows sheets of "small round blue cells"* with scattered "strap cells" or "tadpole cells" having cross-striations (rhabdomyoblasts)(image A) & (image B).
Alveolar RMS shows anastomosing fibrous septa (like lung air spaces) and the tumor cells populate the alveolar spaces.
Express desmin and skeletal muscles markers myoD1 and myogenin.
About 2/3 of alveolar RMS will show t(2;13) and t(1;13).
Prognosis is related to histologic type and tumor stage.
Alveolar RMS has poorer prognosis.
In contrast to pediatric RMS, adult RMS does not appear to respond to multimodal therapy and has a poorer prognosis.
Infrequent (<1%), but LMS together with rhabdomyosarcoma are the most predominant types of prostate sarcomas in adult.
Occur in 40s to 70s, but may occur in younger and pediatric patients.
Most presents with obstructive symptoms; also hematuria and weight loss.
LMS may grow large (mean 9 cm) and replace entire prostate; often is difficult to completely resect the tumor.
Dense fascicles of spindle cells with pleomorphic cigar-shaped nuclei, prominent nucleoli and abundant mitosis; higher grade tumors, fasciculations become vague.
Necrosis is common and tumors may undergo cystic degeneration
Immunohistochemistry: diagnosis confirmed by smooth muscle markers, such as actin+ and desmin+.
Aggressive course with 1-year survival of 55%.
DDX: other spindle cell tumors such as sarcomatoid carcinoma (keratin+), stromal sarcoma (CD34+, actin-), GIST (c-kit+) and SFT (CD34+, actin-).