Spectrum of Second Primary Malignancies in Pediatric and Adult Langerhans Cell Histiocytosis Cases
Authors: Parikh Richa , Go Ronald S. , Goyal Gaurav 
Published: February 2021

Introduction:
Langerhans cell histiocytosis (LCH) is a rare MAPK-ERK pathway driven histiocytic neoplasm that occurs in pediatric as well as adult population. Despite improvement in clinical outcomes, there is some data to suggest an increased propensity to develop second primary malignancies (SPMs) in LCH patients. However, population-based studies analyzing the incidence and spectrum of SPMs in pediatric and adult LCH patients are lacking. In this study, we utilized the Surveillance, Epidemiology and End Results (SEER) database to examine the various SPMs occurring among pediatric and adult LCH cases.
Methods:
We used the November 2018 submission of the SEER 18 registry, which covers ~27.8% of the US population based on the 2010 census, as our database. We used the SEER*Stat version 8.3.6 statistical software to analyze data. We identified cases diagnosed with LCH as their first primary malignancy between 2000 and 2016 using International Classification of Diseases for Oncology edition 3 (ICD-O-3) codes, including LCH NOS (not otherwise specified) (9751/1), LCH (9751/3), LCH, unifocal (9752/1), LCH, multifocal (9753/3), LCH, disseminated, borderline (9754/1) and Disseminated LCH (9754/3). These cases were followed for 180+months, and the standardized incidence ratio (SIR) or relative risk and absolute excess risk (AER) were calculated. We examined the differences in occurrence of SPMs among the pediatric (Age &lt;18 years) and adult population (Age ≥18 years). Additionally, we evaluated the concurrent and prior cancers in LCH patients as an exploratory objective.
Results:
The study included 1392 cases with LCH (Table 1), with median age at diagnosis 8 years (range newborn - 86 years). Out of these cases, 1205 (87%) were diagnosed as LCH and 186 (13%) as disseminated LCH. 936 cases (67%) were diagnosed at age &lt;18 years (pediatric LCH), while 456 cases (33%) were diagnosed at age ≥18 years (adult LCH). The overall age-adjusted incidence rate for LCH was found to be 1 per 1,000,000. The incidence rate was 2.6 per 1,000,000 in pediatric LCH group and 0.4 per 1,000,000 in the adult LCH group.
Out of the entire cohort, 20 (1.4%) cases developed a total of 21 SPMs [SIR 2.07; 95% Confidence Interval (CI): 1.28-3.16]. Median latency period to development of SPMs was 28 months. The pediatric LCH group had an overall higher risk of developing SPMs [SIR 6.42, 95%CI 2.08-14.97] than the general population, especially for hematologic malignancies [SIR 18.76, 95%CI 6.09-43.78], mainly, nodal Hodgkin lymphoma [SIR 60.93, 95%CI 7.38-220.12] and extranodal non-Hodgkin lymphoma [SIR 60.88, 95%CI 1.54-339.2]. No solid tumors were seen in this group. The adult LCH group did not have an overall increased risk of developing SPMs than the general population [SIR 1.71, 95%CI 0.98-2.77], except for Acute Lymphocytic Leukemia (ALL) [SIR 66.29, 95%CI 1.68-369.36] especially 60-119 months from diagnosis of LCH and miscellaneous cancers [SIR 11.43, 95%CI 2.36-33.39] especially 12-59 months after diagnosis of LCH. 62.5% of SPMs that developed in the adult LCH group were solid tumors, however, the overall risk for developing solid tumors was not higher than the general population [SIR 1.2, 95%CI 0.58-2.2], except for carcinoma in-situ of vulva [SIR 62.72, 95%CI 1.59-349.45] 2-11 months from diagnosis of LCH. Overall, tumors of the respiratory system (21%), female breast (13%) and prostate (9%) were the most common malignancies occurring prior to development of LCH whereas tumors of the respiratory system (28%), non-Hodgkin lymphoma (20%) and endocrine system (13%) occurred concurrent to LCH.
Conclusion:
To our knowledge, this is the first comprehensive population-based study assessing the incidence of SPMs in pediatric and adult LCH. Our study shows that the incidence of LCH is higher in the pediatric age group compared to adults. We found an increased risk for hematologic malignancies, specifically for Hodgkin and non-Hodgkin lymphoma in pediatric LCH compared to the general population. Among adult LCH, however, the risk was higher for development of ALL and carcinoma in-situ of vulva when compared to the general population. Our results may help guide survivorship and surveillance strategies among LCH patients. More studies are needed to understand the molecular underpinning leading to increased SPM formation in LCH patients.

Disclosures
No relevant conflicts of interest to declare.