Background: Diffuse large B-cell lymphoma (DLBCL) typically leads to effacement of the nodal architecture by an\ninfiltrate of malignant cells. Rarely (<1%), DLBCL can present with an interfollicular pattern (DLBCL-IF) preserving the\nlymphoid follicles. It has been postulated that DLBCL-IF is derived from marginal zone B cells and may represent a\nlarge-cell transformation of marginal zone lymphoma (MZL), however no direct evidence has been provided to\ndate. Here we describe a rare case of a diagnostically challenging DLBCL-IF involving a lymph node in a patient\nwith a prior history of lymphadenopathy for several years and MZL involving skin.\nCase presentation: A 53-year old man presented to our Dermatology Clinic due to a 1-year history of generalized\nitching, fatigue of 2ââ?¬â??3 monthââ?¬â?¢s duration, nausea and mid back rash that was biopsied. PET (positron emission\ntomography)/CT (computed tomography) was performed and revealed inguinal, pelvic, retroperitoneal, axillary, and\ncervical lymphadenopathy. The patient was referred to surgery for excisional biopsy of a right inguinal lymph node.\nDiagnostic H&E stained slides and ancillary studies were reviewed for the lymph node and skin specimens. B-cell\nclonality by PCR and sequencing studies were performed on both specimens.\nWe demonstrate that this patientââ?¬â?¢s MZL and DLBCL-IF are clonally related, strongly suggesting that transformation\nof MZL to DLBCL had occurred. Furthermore, we identified a novel deletion of the long arm of chromosome 20\n(del(20q12)) and a missense mutation in BIRC3 (Baculoviral IAP repeat-containing protein 3) in this patientââ?¬â?¢s DLBCL\nthat are absent from his MZL, suggesting that these genetic alterations contributed to the large cell transformation.\nConclusions: To our knowledge, this is the first report providing molecular evidence for a previously suspected link\nbetween MZL and DLBCL-IF. In addition, we describe for the first time del(20q12) and a missense mutation in BIRC3\nin DLBCL. Our findings also raise awareness of DLBCL-IF and discuss the diagnostic pitfalls of this rare entity.
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