Contributed by Edward D. Plowey, MD, PhD and Raymond E. Felgar, MD, PhD
The patient is a 66-year-old male with a history of precursor B-cell acute-lymphoblastic-leukemia diagnosed in July. Classical cytogenetic analysis of the bone marrow aspirate demonstrated Trisomy 11 and corresponding 3 signals for the MLL locus on FISH, with no translocation or rearrangement of the MLL gene locus using a break-apart probe. FISH studies were also negative for the BCR/ABL1 gene rearrangement. The patient achieved complete remission after induction chemotherapy in August. He remained in complete remission through maintenance chemotherapy until his presentation in December, with an upper lip mass that was biopsied. Subsequently, a 2 cm lip mass was excised in February, 2008. No evidence of precursor B-cell leukemia was concurrently evident on blood or bone marrow review.
Histologic sections of the tumor demonstrate a soft tissue neoplasm comprised of intermediate to large epithelioid cells with moderate to abundant, pale to eosinophilic, finely granular cytoplasm. The tumor cells show eccentrically located, oval to reniform nuclei with irregular nuclear membrane contours but mostly vesicular chromatin and occasional prominent nucleoli. Only occasional mitotic figures are seen. The majority of the tumor demonstrates a solid growth pattern but at the periphery, the tumor cells show an infiltrative growth pattern, growing between skeletal muscle fibers and adipocytes, encasing nerve branches and infiltrating into minor salivary gland. Tumor necrosis was also seen.
Paraffin section immunohistochemical stains show that the tumor is diffusely and weakly positive for CD45 (leukocyte common antigen, LCA) and CD4, with strong positivity for CD68 (PGM-1), CD14, CD163 and fascin. Lysozyme was focally positive. Ki-67/MIB-1 labeled 40-50% of the tumor nuclei. The tumor was negative for B-cell markers (CD20, CD79a, PAX5) and TdT. Additional pertinent negative stains include CD3, CD30, ALK-1, CD123, CD23, CD21, CD1a, S100, tyrosinase and a pancytokeratin cocktail.
FLUORESCENCE IN-SITU HYBRIDIZATION (FISH):
FISH testing for the MLL locus using a break-apart probe indicates the presence of 3 intact signals in 34% of the nuclei analyzed, consistent with Trisomy 11. No rearrangements involving the MLL gene locus were present.