EP386 - Zebra in the Rectum: A Rare Case of Primary Rectal Lymphoma

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Purpose/Background: Lymphomas are non-epithelial hematologic malignancies that arise from clonal proliferation of lymphocytes. They are classified as nodal or extra-nodal based on disease site. Although overall extra-nodal lymphomas are commonly found in the gastrointestinal tract, colorectal lymphomas are uncommon. Rectal lymphoma is very rare and represents < 0.001% to 0.3% of all rectal malignancies. Risk factors for colorectal lymphoma include an immunosuppressed state and conditions that lead to chronic inflammation such as inflammatory bowel disease. Here we describe a case of primary rectal large B-cell lymphoma.

Methods/Interventions: A 20-year-old female with medical history significant for excision of a dysplastic nevus presented with 3 months of bright red blood per rectum noted both on toilet paper and in the bowl. Her bleeding increased in volume prompting evaluation. She denied rectal pain, changes in bowel habits, fevers, chills, or night sweats. Colonoscopy demonstrated a 5cm ulcerated rectal mass overlying the distal rectal fold with no other lesions noted in the colon or rectum. Pathology was only consistent for an undifferentiated mass. Patient subsequently presented for tertiary evaluation. Rectal examination revealed a tethered, fleshy mass. Office flexible sigmoidoscopy notable for right anterior, atypical lobular, and centrally ulcerated mass 5cm from the anal verge. Due to prior ambiguous findings, suspicion for lymphoma was raised and biopsies obtained were placed in both formalin and RPMI medium. Magnetic resonance imaging (MRI) of the pelvis demonstrated a right anterior mid rectal lesion with approximately 6mm of extramural invasion and no lymphadenopathy. Flow cytometry showed clonal lambda restricted CD10+/CD20+ B-cell population and pathology consistent with large B-cell lymphoma, germinal center phenotype with high proliferation fraction (Ki-67) of 95%.

Results/Outcomes: Differential includes diffuse large B-cell lymphoma versus high-grade B-cell lymphoma with Myc and BCL-2 gene rearrangements, and with Burkitt lymphoma being less likely. Fluorescence in situ hybridization (FISH) testing to clarify final pathology is pending. Staging computed topography (CT) of the chest, abdomen, and pelvis obtained with no evidence of lymphadenopathy or other organ involvement. Positron emission topography-computed topography (PET-CT) obtained with intense metabolic activity in the known rectal lesion and intense metabolic activity in the tonsils bilaterally, deemed physiologic for her age. Bone marrow biopsies and lumbar puncture for cerebrospinal fluid analysis are pending. Medical oncology is planning to initiate multi-agent chemotherapy with final regimen pending results of FISH testing.

Conclusion/Discussion: Primary diffuse large B-cell lymphoma of the rectum is extremely rare, with very few documented cases. The aggressive nature of these tumors necessitates prompt diagnosis and treatment. Our patient presented with rectal bleeding and was otherwise asymptomatic. She has no known risk factors for the development of lymphoma and was significantly younger than the age of typically lymphoma diagnosis. Our case adds to the limited body of evidence about the presence, diagnosis, and treatment of a rare rectal malignancy.