Discussion:
Lymphoblastic lymphoma (LBL) is an uncommon non-Hodgkin lymphoma and accounts for only 5% of all non-Hodgkin’s lymphoma. According to the WHO classification, LBL is distinguished from acute lymphoblastic leukemia (ALL) by a bone marrow blast count of less than 20% of nucleated cells 1. It can be of T-cell or B-cell lineage. B-cell LBL (B-LBL), the rarer subtype, is a high-grade neoplasm of immature B cells that demonstrate lymphoblastic morphology and express precursors and B-cell markers 2. It accounts for less than 10% of cases of lymphoblastic lymphoma. In contrast to T-cell LBL, B-LBL tends to involve skin and bone and to spare mediastinal lymph nodes. Primary cutaneous precursor B-LBL (PB-LBL) is exceedingly uncommon in children and seems to occur more frequently in young females 3. It usually presents as solitary red to purple nodules with a propensity for the head and neck area4.
Histologically, there is an overlap between B-LBL and other lymphoid malignant neoplasms mainly precursor T-cell LBL, and ‘small blue round cell’ neoplasms such as Ewing’s sarcoma, rhabdomyosarcoma, and neuroblastoma, rendering histopathological diagnosis difficult. Thus, IHC is crucial and very useful to rule out differential diagnoses. Indeed, the expression of TdT and CD34 and the absence of CD20 markers on B-lineage lymphomas suggest their precursor B-cell origin, as in our case 3.
Although PB-LBL is a highly aggressive malignant neoplasm, its prognosis is dramatically improved with the use of aggressive multi-agent chemotherapy ALL-regimens with up to 90% of 5-year EFS rate3. Partial remission, as seen in our case despite an aggressive multi-agent systemic chemotherapy, is rare.
In conclusion, this case serves as an important reminder for clinicians to consider this entity as a potential differential diagnosis for head and neck tumors especially in the pediatric population.