Surgically Treated Retroperitoneal Sarcoma: A Population-based Competing Risks Analysis

Background: Data regarding the relationship between non–disease-specific (NDSM) and disease-specific mortality (DSM) in patients with surgically treated nonmetastatic retroperitoneal sarcoma (nmRPS) are lacking. Objective: To examine the rates of NDSM and DSM among patients with surgically treated nmRPS. Design, setting and participants: We used the Surveillance, Epidemiology and End Results (SEER) database (2004–2014) to obtain data for patients with surgically treated nonmetastatic RPS. Outcome measurements and statistical analyses: The 5-yr DSM and NDSM rates were generated via competing risks regression (CRR) methodologies. Multivariable CRR models were used to test the effects of age, histologic subtype, grade, size, and radiotherapy (RT) status on NDSM and DSM. Results and limitations: Overall, 231 (26.8%) and 57 patients (6.7%) died from DSM and NDSM, respectively. Following stratification according to age, histologic subtype, grade, size, and RT status, the proportion of patients who succumbed to NDSM was higher for patients with age above the median, liposarcoma histologic subtype, low grade, and tumor size ≥17 cm. DSM rates were also higher among patients with age above the median, leiomyosarcoma histologic subtype, high grade, and tumor size ≥17 cm. Multivariable CRR models revealed that age above the median was associated with higher NDSM (hazard ratio [HR]1.7, 95% confidence interval [CI] 1.1–2.7; p = 0.019). Conversely, leiomyosarcoma (HR 1.9, 95% CI 1.4–2.6; p < 0.0001), sarcoma not otherwise specified (HR 2.4, 95% CI 1.5–3.8; p < 0.0001) and other RPS (HR 2, 95% CI 1.2–3.4; p = 0.01) histologic subtypes, high grade (HR 3, 95% CI 2.3–4; p < 0.0001), and tumor size above the median (HR 1.4, 95% CI 1.1–3.8; p = 0.012) were associated with higher DSM. This is a retrospective study and misclassification bias may be present because of the reliability of the distinction between DSM and NDSM. Conclusions: The impact of NDSM in surgically treated nmRPS is not trivial, particularly among patients with favorable characteristics such as liposarcoma histologic subtype and low-grade tumors. Patient summary: Mortality from causes not related to the specific disease is important in patients with retroperitoneal sarcoma (RPS) treated surgically. In particular, patients with good tumor characteristics, namely liposarcoma histologic subtype and low grade, most often do not die from their cancer but succumb to causes other than RPS. Unfortunately, tumor characteristics and radiotherapy administration shed relatively little light on predicting mortality from causes other than cancer in patients with surgically treated RPS. Our report compares the risk of dying from RPS with that of dying from other causes according to the type of surgically treated sarcoma. An important proportion (20%) of all deaths among patients with surgically treated retroperitoneal sarcoma can be attributed to other causes, and this fact need to be discussed with patients. Specifically, among patients with favorable characteristics such as low grade and liposarcoma histologic subtype, the higher probability of dying from causes other than retroperitoneal sarcoma at 5 yr represents a source of reassurance regarding the natural history of their surgically treated disease.