Smooth muscle tumours of the urinary bladder

Epidemiology

Leiomyosarcoma is the most common malignant mesenchymal tumour of the urinary bladder.

Histopathology

The criteria for distinguishing between benign and malignant smooth muscle tumours are not yet well established.

leiomyoma; reserved for tumours with well circumscribed margins, of low cellularity and absent to minimal mitotic activity¹.

• low grade leiomyosarcoma; < 5 mitoses / 10 HPF - none of 10 cases recurred or metastasised¹.

• high grade leiomyosarcoma; > 5 mitoses / 10 HPF - 2 of 5 patients died¹.

Immunohistochemistry

	leiomyoma	leiomyosarcoma
vimentin	17/181	9/91
smooth muscle actin, 1A4	12/181	9/91
muscle-specific actin, HHF35	14/181	9/91
both smooth muscle actin and muscle-specific actin	11/181	9/91
desmin	7/181	9/91
AE1/AE3	0/181	0/91
Cam5.2	0/181	0/91
wide-spectrum keratin, polyclonal	0/181	0/91
cd117, c-kit	3/181	0/91
CD34	2/18: two cases positive for both CD34 and CD117 were also positive for both smooth muscle actin and muscle-specific actin1	3/91
S-100	0/181	0/91

Differential diagnosis of leiomyosarcoma of urinary bladder

• inflammatory pseudotumour (inflammatory myofibroblastic tumour)

• postoperative spindle cell nodule

• sarcomatoid carcinoma

References

¹Martin, S. A., Sears, D. L., Sebo, T. J., Lohse, C. M., Cheville, J. C. Smooth muscle neoplasms of the urinary bladder: a clinicopathologic comparison of leiomyoma and leiomyosarcoma. Am J Surg Pathol 2002;26:292-300

This page last revised 1.5.2002.

©SMUHT/PW Bishop