Discussion
Lymphoblastic lymphomas (LBL) are a neoplasm of immature B cells
belonging to the B-(B-LBL) or T-cell lineage (T-LBL) that account for
approximately 2% of all lymphomas and for approximately 8% of all
lymphoid malignancies [5]. LBL is more prevalent in males compared
to females, with a male/female prevalence of 1.4. The highest rate of
occurrence was reported in children younger than 15 years old with a
rate of 3.6 per 100,000; followed by 0.8 per 100,000 in patients aged
between 25 to 64 years old; and then increased to 1.7 per 100,000 in the
oldest age group of cases older than 65 years old [2]. It commonly
develops in children and young adults and presents as multiple purple
nodules or papules within the head and neck region. Most cases have no
constitutional symptoms [6]. In most cases, skin lesions are
secondary to or concomitant with bone, bone marrow, or lymph node
involvement. Furthermore, cutaneous involvement at the time of
presentation is usually rare which further fortifies the rarity of our
case [7]. Differential diagnosis of LBL include blastoid variant of
mantle cell lymphoma, Burkitt lymphoma or myeloid leukaemia which may
arise in some particular adult cases [2]. Histological presentations
are usually sufficient in order to distinguish lymphoblastic from mature
B- or T-cell neoplasms, however the key for diagnosis is the
characterization of immunophenotype by flow cytometry [8].
Lymphoblastic lymphoma (LBL) is similar to acute lymphoblastic leukemia
(ALL) and the differentiation between these neoplasms is based upon
proportion of involvement of lymphoblasts in bone marrow
(<25% for lymphoblastic lymphoma and >25% for
ALL) [9]. It has a higher male to female predominance (except female
preponderance in B-type) with a ratio of 1.4:1 [5], higher incidence
in older children and younger adults, and a relatively higher frequency
of CNS and gonadal involvement in the course of the disease. With the
same chemotherapy regimen, patients with B-LBL have more complete
remission (CR) and rarely develop leukemia compared to those with ALL.
Furthermore, the survival rate is higher in patients who had a complete
response to chemotherapy than that of patients with partial or no
response to chemotherapy [11, 12]. In terms of histopathological
characteristics, cutaneous lymphoblastic lymphoma shows heavy
infiltrates of atypical cells among collagen bundles with scant
cytoplasm and prominent nucleoli. A focal or diffuse starry-sky pattern
may be present. Cutaneous involvement is present in 33% of patients
with B-LBL and 1% of patients with B-cell ALL that is considered as
leukemia cutis [13]. Immunohistochemistry is necessary to rule out
possible differential diagnosis including leukemic infiltration of acute
myeloid leukemia (AML), T-cell ALL, Ewing sarcoma, primitive
neuroectodermal tumor, neuroblastoma, small cell melanoma, Merkel cell
carcinoma and Burkitt lymphoma. Utilizing IHC staining for Bcl-2, Bcl-6,
and TdT, LBL can be differentiated from Burkitt lymphoma. Bcl-6 is
negative in LBL, while Bcl-2 and TdT are negative in Burkitt lymphoma
[14].