Characteristics and Clinical Outcomes in Multiple Myeloma in a Distinct Demographic: Adolescents and Young Adults
Authors: Olafimihan Ayobami , Jackson Inimfon , Ugwuja Ferdinand , Fawehinmi Praise , Farooqui Marwah 
Published: December 2024

Background
Multiple myeloma (MM) is the second most common adult hematologic malignancy in the United States, and while the median age at diagnosis is 69 years, multiple myeloma can also occur in adolescents and young adults (AYA) aged 15 to 39 years. Though it is less frequent in this population, it is important because AYAs with MM have a different disease biology than the older patients and outcomes in this population are unknown. We examined the inpatient characteristics and outcomes for AYA patients with a diagnosis of MM.
Methods
In a retrospective cohort analysis using the Nationwide Inpatient Sample (NIS) database from 2008 to 2021, patients with non-elective primary hospitalizations for multiple myeloma were identified using ICD-9 and ICD-10 codes. Descriptive analyses were conducted using STATA version 17.0 to compare sociodemographic, hospital-level and clinical characteristics between AYA and older populations. Multivariate logistic and linear regression models were used to examine the association between the age groups and inpatient mortality, length of stay (LOS), and total hospital charges. All P values were two-sided, with a significant level set at 0.05.
Results
There were 143,856 non-elective hospitalizations for multiple myeloma within the 14-year study period. Of these, 1,796 (1.2%) were in the AYA cohort. The mean age was 34.7 years in the AYA group and 67.3 years in the older group (P &lt; 0.001). There was a higher proportion of males in the AYA group compared to the older group (63% vs 55%, P = 0.003) but a lower distribution of Caucasians (35% vs 56%, P &lt; 0.001). Most of the patients in the AYA population had private insurance (47.3%), while the older adults were on Medicare (59.2%, P&lt;0.001). Both groups had more admissions in teaching hospitals (82.9% vs 70%, P &lt; 0.001), and were located in the southern region (40% vs 38%, P=0.04). Additionally, most AYA patients had lower Charlson Comorbidity Index scores (0-2) than the older patients (61% vs 34%, P &lt; 0.001).
Regarding clinical characteristics, AYA-MM patients had a lower frequency of chronic kidney disease (16% vs 32.6%, P &lt; 0.001), anemia (20.1% vs 28%, P &lt; 0.001), and acute venous thromboembolism (1.1% vs 3.2%, P=0.02). However, the occurrence of hypercalcemia, pathological fracture, light chain amyloidosis and severe sepsis were similar between both populations.
The mortality rate was lower in the AYA population compared to the older population (2.2% vs 7.4%, P = 0.001). On multivariate logistic regression, the AYA group had 70% lower odds of mortality relative to the older adult group (adjusted odds ratio [aOR]: 0.28, 95% confidence interval [CI]: 0.14-0.57, P &lt; 0.001). Although there was a tendency towards higher odds of a longer hospital stay in the AYA group, this was not significant (aOR: 1.07, 95% CI: 0.87-1.33, P = 0.51). Hospital expenditures were similar between the two cohorts (β-Coefficient: 15,125, 95% CI: -4,165-34,416, P = 0.12). The odds of receiving autologous stem cell transplant (ASCT) were two-fold higher in the younger group compared to their older counterparts (aOR: 2.10, 95% CI: 1.55-2.83, P&lt;0.001).
Conclusion
To the best of our knowledge, this is the largest epidemiological study to date on multiple myeloma hospitalizations in AYA. AYAs with MM are more likely to undergo ASCT and have lower odds of mortality relative to older adult MM patients. Our findings highlight the unique characteristics and outcomes that could improve patient selection for future clinical trials and optimize the development of novel therapies for this population.