Hematopathology
Davsheen Bedi, MD and Nidhi Aggarwal, MD
Case Presentation
A Caucasian male in his twenties presented with a left abdominal pain and discomfort since a few weeks. There was no history of night sweats, fevers, or weight loss. CT scan of the abdomen revealed a 4.5 x 1.7 x 2.3 cm lobulated, non-vascular, soft tissue density on the left side of the aorta, below the level of the renal vessels. Initial radiologically guided fine needle aspiration (FNA) and biopsy were too small and non- representative. All serological markers for a germ cell neoplasm were negative and a scrotal ultrasound performed was unremarkable.
The patient presented again six years later with a left lower back pain, radiating down the left leg. CT scan performed revealed an increase in the size of the paraspinal mass to 10.1 x 6.5 cm (Figure 1A), with invasion into adjacent psoas muscle and enlargement of other peri-aortic lymph nodes. A CT guided biopsy performed showed sheets of large atypical cells with moderate pleomorphism, variably shaped nuclei, some with "horse-shoe shaped" nuclei and with abundant vacuolated cytoplasm (Figure 1B). Touch imprints prepared from the needle cores also showed these large atypical cells with bubbly vacuolated cytoplasm (Figure 1C). Some mitotic figures and multi-nucleated cells with prominent nucleoli were also noted.
On immunohistochemistry, the tumor cells were weakly positive for Leucocyte Common Antigen (LCA) (Figure 2A) and negative for both CD20 (Figure 2B) and CD3 (Figure 2C). In order to rule out a carcinoma, several keratin immunostains were performed, i.e. pan keratin, CK7, CK20, AE1/AE3 and CAM 5.2 of which all were negative, except for CAM5.2 which was weakly positive in some of the large atypical cells (Figure 2D). EMA (Figure 3A) and CD30 (Figure 3B) were also positive in the large atypical cells. ALK immunostain performed showed strong, diffuse nuclear and cytoplasmic positivity in the tumor cells (Figure 3C). However, none of the immunostains for T-cells were positive, i.e. CD2, CD3, CD5, CD7, CD4, CD8 and CD43. While TIA (T-cell intracytoplasmic antigen) was also negative, granzyme showed positivity in the tumor cells (Figure 3D). Additional immunostains performed to rule out other possibilities like Hodgkin lymphoma (PAX5, OCT2, BOB1), histiocytic neoplasm (CD68), germ cell tumor (CD117, OCT3/4, SALL4), metastatic lung carcinoma (P40, TTF1), metastatic gastrointestinal carcinoma (CDX2), sarcoma (actin, myogenin, desmin), melanoma (SOX10, Melan, HMB45), nerve sheath tumor (S100), etc. were negative.
Molecular studies performed were positive for T cell rearrangement, raising concerns for T cell lineage even though the IHC markers were negative. Further, cytogenetic florescence in-situ hybridization (FISH) studies using break apart probe for ALK showed four copies of ALK gene, two of which were rearranged.
The patient did not have any other lymphadenopathy or bone marrow involvement.
