Abstract
Background:
Splenic marginal zone lymphoma (SMZL) is a rare indolent B cell neoplasm. There has been limited information to date at the population level on variation by racial, socioeconomic, and geographic subgroups in incidence and outcomes. Awareness of these trends can be helpful in planning outreach that should result in enhanced equity in diagnosis and treatment.
Methods:
The SEER Research Data (17 registries) linked with county attributes (income and rurality) for 2000–2022 were analysed. A rate session provided age adjusted incidence rates per 100 000 population by race (White, Black, Asian/Pacific Islander [API], American Indian/Alaska Native [AI/AN]), sex, county level socioeconomic status (SES; high, mid, low), and rural urban continuum code (urban, suburban, rural). A frequency session summarised the distribution of cases by age group and sex. Relative survival was estimated from a survival session using actuarial methods, producing five year observed and relative survival for combinations of SES and geography. Treatment data were not available in these exports, so management patterns could not be assessed.
Results:
Incidence patterns -
Overall frequency: 3,545 SMZL cases were identified between 2000 and 2022. Incidence increased modestly over time, rising from ~0.05 per 100 000 in 2000 to ~0.28 per 100 000 in 2022.
Race: Age adjusted incidence was highest among White patients (0.225 per 100 000) compared with Black (0.072), API (0.076) and AI/AN (0.042) populations. Whites accounted for ~90 % of cases.
Sex: Women experienced a slightly higher incidence than men (0.198 vs. 0.176 per 100 000), but counts were similar (1882 females vs. 1636 males).
Socioeconomic status: High SES counties had a modestly higher incidence (0.231 per 100 000) than mid SES (0.187) or low SES counties (0.177). This translated into 272 cases in high SES, 2449 in mid SES and 796 in low SES counties.
Geography: Rural counties showed the highest incidence (0.292 per 100 000) despite having far fewer cases (201) and a smaller population; suburban and urban counties had lower rates (0.212 and 0.183 per 100 000). Total counts were highest in urban areas (3072 cases), reflecting increased diagnosis likely secondary to proximity and more access to medical care.
Age distribution -
Age specific frequencies revealed that SMZL predominantly affects older adults. Nearly three-quarters occurred in patients aged 70 years and above; the largest number was in the 70–74 years' group. Cases below 50 years of age were extremely rare.
Survival analysis -
Relative survival analysis was summarized by five year outcomes and showed a significant racial disparity, five year relative survival was 75.7% in Black patients vs 87.2% in White patients, with non overlapping 95% confidence intervals. Differences by SES and geography were more modest: 87.6% in mid SES urban, 85.7% in high-SES urban, 84.8% in low SES urban, and 79.5% in low SES rural; for the latter, the observed five year overall survival was ~68%, and most SES subgroup CIs overlapped. By sex, five year relative survival was 88.7% in females and 84.5% in males, a difference not statistically significant.
Conclusion :
This SEER analysis confirms that SMZL remains an exceedingly rare lymphoma that overwhelmingly affects older adults. White patients and those living in high SES or rural counties have marginally higher age adjusted incidence, whereas non White groups experience lower incidence. Five year relative survival is quite good throughout SES and geography, with only minimal decrements in low SES rural populations. These findings suggest that, although incidence varies by race and socioeconomic setting, disparities in survival are less pronounced. Further investigations linking individual level socioeconomic and treatment data are needed to examine the causes for these disparities and to ensure equitable care for all SMZL patients.
