Secondary peritoneal and retroperitoneal malignancies in the elderly: trends and disparities (1999-2022) with...

Secondary malignant neoplasms of the retroperitoneum and peritoneum (SMNRP) indicate advanced disease and poor prognosis, yet their population-level mortality patterns remain underexplored. This study analyzed national trends and disparities in SMNRP-related mortality among US adults, forecasted future trends, and examined age-adjusted incidence and mortality rates (AAIRs and AAMRs) for the 10 primary cancers most frequently associated with SMNRP.

This cross-sectional study used data from CDC WONDER (1999-2022) and US Cancer Statistics. We assessed temporal trends in SMNRP-related (ICD-10: C78.6) mortality in US adults aged ≥ 65, stratified by demographics, primary site of malignancy, and geography. AAMRs, AAIRs, and crude mortality rates (CMRs) were calculated per 100,000 population. Trends were analyzed using the Joinpoint Regression Program to estimate annual and average annual percent changes (APC and AAPC). Future trends were projected through 2035 using ETS and ARIMA models.

SMNRP-related AAMRs increased significantly from 1999 to 2022, rising from 3.3 to 12.4 per 100,000 (AAPC = 5.86%, 95% CI 5.56-6.29). Of the 61,583 deaths, 66.1% were females, with higher AAPCs (6.14%, 95% CI 5.93-6.35) than males (5.37%, 95% CI 4.75-6.15). Stratification by primary cancer site showed ovarian (12.9%) and colon (11.6%) cancers as the leading causes of death. AAIRs and cancer-specific AAMRs (irrespective of SMNRP) declined for most cancers. All racial groups showed ≥ threefold increases in AAMR, with Non-Hispanic Whites having the highest AAPC (6.00%, 95% CI 5.60-6.42). The 85 + age group had the highest CMRs. Regionally, the West showed the steepest increase. Urban areas consistently had higher AAMRs. Forecasting models projected AAMRs to reach ~ 24.5 per 100,000 by 2035.

SMNRP-related mortality has increased substantially among older US adults. As primary cancer outcomes improve, longer survival increases the risk of metastatic recurrence and progression. Enhanced detection, surveillance, and management are needed.