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.