Pediatric Precursor B-Cell Lymphoblastic Malignancies: From Extramedullary to Medullary Involvement

SIMPLE SUMMARY: B-cell lymphoblastic lymphoma (BCP-LBL) and B-cell acute lymphoblastic leukemia (BCP-ALL) are both malignancies of immature B-cells. However, BCP-ALL has been extensively studied and treatment protocols have changed over the last decades, whereas BCP-LBL is quite rare, and treatment has stayed roughly the same. In this retrospective study, we compare the clinical characteristics of a cohort of BCP-LBL patients to a cohort BCP-ALL patients. With the comparison of this unique large cohort of immature B-cell malignancies, we aim to contribute to elucidating whether BCP-LBL and BCP-ALL represent two diseases, or different representations of the same disease. Increasing the understanding of BCP-LBL in comparison to BCP-ALL is crucial for improving treatment and prognosis for BCP-LBL. ABSTRACT: B-cell lymphoblastic lymphoma (BCP-LBL) and B-cell acute lymphoblastic leukemia (BCP-ALL) are the malignant counterparts of immature B-cells. BCP-ALL is the most common hematological malignancy in childhood, while BCP-LBL accounts for only 1% of all hematological malignancies in children. Therefore, BCP-ALL has been well studied and treatment protocols have changed over the last decades, whereas treatment for BCP-LBL has stayed roughly the same. Clinical characteristics of 364 pediatric patients with precursor B-cell malignancies were studied, consisting of BCP-LBL (n = 210) and BCP-ALL (n = 154) patients. Our results indicate that based on the clinical presentation of disease, B-cell malignancies probably represent a spectrum ranging from complete isolated medullary disease to apparent complete extramedullary disease. Hepatosplenomegaly and peripheral blood involvement are the most important discriminators, as both seen in 80% and 95% of the BCP-ALL patients and in 2% of the BCP-LBL patients, respectively. In addition, we show that the overall survival rates in this cohort differ significantly between BCP-LBL and BCP-ALL patients aged 1–18 years (p = 0.0080), and that the outcome for infants (0–1 years) with BCP-LBL is significantly decreased compared to BCP-LBL patients of all other pediatric ages (p < 0.0001).