Epidemiological analysis of mycosis fungoides (MF) in children and young adult patient populations: A population‐based analysis of the nationwide surveillance, epidemiology and end results (SEER) database

Epidemiologic data for mycosis fungoides (MF) in the paediatric (0–19) and YA (20–29) patients are scarce. We analysed epidemiologic data from SEER, a nationwide database, and are reporting trends for these underreported US patient populations. Using the SEER Database (2000–2020), data for patients aged 0–29 years with a diagnosis of MF (ICD-code: 9700/3) were collected. Extracted data were then stratified by age group in years (children: 0–19 and YA: 20–29). Incidence rates (IRs), IR trends (as annual percent change [APC]) and the risk of developing a secondary-primary malignancy (SPM) were calculated. Data for patients with a SPM within 60 days of diagnosis for MF were excluded. The risk for SPMs was analysed by calculating the standardized incidence ratio (SIR), a ratio of the observed cancer incidence in the MF cohort compared to the expected incidence in the age, sex and race-matched general population (O:E ratio), derived from the United States Census Bureau. 95% CIs were calculated. SEER*Stat software1 was used for data collection and analyses. There were 9138 MF cases in SEER, 712 (7.8%) constituted data for patients up to age 29. Of the 712 patients, 285 (40%) were children and 427 (60%) were YA; 366 (51%) were male (paediatrics: 41%; YA: 59%) and 346 (49%) were female (children: 39%; YA: 61%) (Table 1). The age-adjusted IR was 0.96 (95% confidence interval [CI], 0.9–1.0) per million persons (IR, 0.6 for children and 1.7 for YA). No significant difference was detected by sex for IRs across both groups. MF in the entire YA population (age 0–29) had an increasing IR trend (APC: 5.1%, 95% CI: 3.2–7.1, p < 0.05). Moreover, IR trends differed (Figure 1) between children (APC: 7.2%, 95% CI: 4.6–9.8, p < 0.05) and YA groups (APC: 3.7%, 95% CI: 1.5–5.9, p < 0.05). Both children and YAs had significantly higher trends when compared to patient populations older than 29 years (N = 8426; APC: 1.9% for those 30–59 yo, APC: 3.6% for those >60 yo). The APC for all ages was 3.0%. From the children cohort, four patients (1.5%) developed at least one or more subsequent SPM, while the YA cohort had 14 patients (3.2%) developed at least one or more subsequent SPM. YA (O:E 4.1, 95% CI 2.26–6.95, p < 0.05) and children (O:E 5.65, 95% CI 1.54–14.47) showed an increased risk of a SPMs. Notably, cancer of the corpus uteri was the only detected SPM occurring in children 0–19 (1 reported case). Other reported SPMs, including lymphomas and leukaemias, may still represent an evolution of the primary disease process or side effect from MF treatment (Table 1), though there is no definitive method to confirm. Moreover, only the YA population had a statistically significant mortality rate from all malignant cancers at 1 year (O:E 47.30, 95% CI 1.20–263.55), 5 years (O:E 33.31, 95% CI 6.87–97.34), 10 years (O:E 25.74, 95% CI 5.31–75.21) and across all years (O:E 17.44, 95% CI 7.01–35.93), and from all causes of death across all years (O:E 3.26, 95% CI 1.74–5.58). Again, a possible explanation for this increased risk may be delays in presentation and diagnosis for YA patients, consistent with prior studies of cancer disparities.2 Even after diagnosis, YA patients may have poorer cancer outcomes due to variability in treatment protocols between adult and paediatric patients, challenges to enrolment in clinical trials and a greater likelihood of noncompliance.3-5 As trends for MF continue to increase in young adults and paediatrics patients, enhanced monitoring seems warranted for the detection of a second primary malignancy, especially in young adults 20–29 years of age, perhaps, as an example, through the use of guidance from the American Cancer Society's survivorship guidelines.6 None. None declared. Exempt from review. Not applicable. The data that support the findings of this study are available from the corresponding author upon reasonable request.