American Urological Association - Smooth Muscle Tumors
Smooth Muscle Tumors
- May arise from periglandular tissues or prostatic capsule.
- Rare, most occur in 60s presenting with obstructive symptoms.
- May be mistaken clinically as BPH and encountered often in TUR.
- Typically, solitary 2-7 cm, but can grow considerably large (>10 cm).
- Gross: solitary, well circumscribed, white-tan with smooth outer surface.
- Traditionally described in 2 forms, as solitary tumors and in background of BPH. (Those in BPH were probably "leiomyomatous" type hyperplasia).
- Histology: fascicles of benign spindle cells with cigar-shaped nuclei.
- Immunohistochemistry: smooth muscle marker actin+ and desmin+.
- Rarely, exhibits polygonal or round cell morphology (leiomyoblastoma).
- DDX: leiomyomatous BPH (multiple) and other spindle cell tumors.
- 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-).