Leiomyosarcoma of the urinary bladder: A SEER database study and comparison to leiomyosarcomas of the uterus and extremities/trunk.

No well-established staging system exists for bladder leiomyosarcoma (LMS), and the current staging system does not include tumor size, a thoroughly validated prognostic parameter for sarcomas. Uterine and extremity/trunk LMS are more common than those in the bladder and have well-established staging systems incorporating tumor size. We aim to improve the understanding of LMS of the urinary bladder by assessing cancer-specific survival (CSS) and comparing LMS at this unusual anatomic site to those arising at other sites using the Surveillance, Epidemiology, and End Results (SEER) database. The SEER database (1973-2013) was queried for bladder, uterus, and trunk/extremity LMS. Multivariable Cox proportional hazard regression was performed to identify predictors of CSS for each anatomic location and used to compare outcomes at different sites. We identified 165 bladder, 4987 uterus, and 2536 extremity/trunk LMS cases. Five-year CSS was 52% for uterus, 73% for bladder, and 82% for extremity/trunk LMS. For LMS at all sites, uterine location (HR = 2.14, P < 0.001) and increasing tumor size (HR = 1.05, P < 0.001) were significant predictors of worse CSS on multivariate analysis. For bladder LMS, increasing tumor size (HR = 1.18, P = 0.003) was an independent prognostic factor and the conventional staging cut-off threshold of 5 cm for sarcomas outside the head/neck showed statistical significance in stratifying patient risk of cancer-related death. Bladder LMS appears to have clinical behavior intermediate between those of the extremities/trunk and uterus. We suggest that the conventional sarcoma staging protocols based on tumor size be applied to LMS of the urinary bladder.