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].