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Primary Mantle Cell Lymphoma of the Tonsil: A Case Series

Background:
 Mantle cell lymphoma (MCL) is a mature B cell non- Hodgkin lymphoma (NHL) characterized by the t (11; 14) (q13; q32) translocation, which results in over-expression of cyclin D1. It comprises about 7% of NHL in the United States and Europe and its overall incidence appears to be increasing in the United States.
 While most patients present with advanced stage and generalized lymphadenopathy, 25% of patients with MCL present with extra-nodal disease. The most common site of involvement being gastrointestinal tract, liver and bone marrow. Isolated involvement of waldeyer's ring is rare. To date, only a few cases have been reported in the literature.
 Here we describe three patients with primary MCL of the tonsil, summarizing their presentation and clinical course.
 Method:
 We present a case series of MCL of the tonsils diagnosed and followed at a single center from August 2019-May 2020. Data regarding demographics, morphology, IHC stains, clinical presentation, radiographic findings, management and outcome are reviewed.
 Results:
 Three patients were diagnosed with tonsillar MCL. Clinical findings are summarized in table 1. All were men with a mean age of 63 years at diagnosis. None had B symptoms. They presented initially with swallowing difficulty and underwent tonsillectomy. They were found to have low risk pathology and clinical features suggesting the indolent form of MCL.
 Case 1:
 A 73 year-old with history of MEN-2 disorder presented with swallowing difficulty. A left tonsil mass was noted on examination and he underwent left tonsillectomy. Pathology confirmed diagnosis of MCL of the tonsil, with positive IHC stain for CD5, PAX5, cyclin D1 and SOX11, negative for CD10. The Ki-67 proliferative index was approximately 10-15%. PET-CT did not show any evidence of disease except for few non-specific level 1b and III left cervical nodes. Patient declined further staging work up, including a bone marrow biopsy and biopsy of a small left cervical lymph node to exclude other sites of involvement. He remains symptom-free on observation.
 Case 2:
 A 61 year-old presented with intermittent chocking sensation and difficulty swallowing. An enlarged right tonsil was observed on examination. He underwent right tonsillectomy and pathology was consistent with MCL, with positive IHC stain for CD5, cyclin D1 and SOX11, negative for CD 10. Ki-67 proliferative index was 30% and TP53 mutation was negative. Bone marrow evaluation showed 30% involvement with MCL, however, his peripheral cell counts were normal. PET-CT did not show any convincing evidence for other sites of involvement. We recommended watchful waiting and patient remains symptom free on close follow up.
 Case 3:
 A 55 year-old presented with dysphagia and sensation of a lump in his throat. He was noted to have bilateral tonsil enlargement. He underwent bilateral tonsillectomy. Pathology showed a population of B-cells with kappa light chain restriction and co-expression of CD5 and SOX 11 on the left tonsil only, consistent with diagnosis of MCL of left tonsil. The Ki-67 proliferative index was 20%. Bone marrow evaluation showed low level of involvement ~1% by MCL. PET-CT did not show any convincing evidence of disease elsewhere. We recommended watchful waiting and patient remains symptom free on close follow up,
 Conclusion:
 Primary MCL of the tonsils is an uncommon diagnosis. To the best of our knowledge this is the largest case series of this rare disease reported by a single institution.
 The demographics, histology and molecular features of our patients are similar to published data on MCL. Mainstay of therapy for MCL remains combination chemo immunotherapy which is not considered curative. Some studies have showed a prolonged median survival of 7 years in MCL patients treated nonaggressively, suggesting that a subset of patients may have an indolent course. Identification of this unique group of patients is challenging as there is no validated prognostic tool yet. In addition to MIPI, the Ki-67 score seems to be a powerful predictor of survival, with scores less than 30% showing prolonged survival.
 Our three patients presented with low Ki-67 score and low burden disease. They did not have B symptoms and were asymptomatic after surgery. Further studies are needed to assess whether MCL of the tonsil, without other dominant systemic disease, represents a unique clinical entity that predicts the indolent form of the disease which could be managed conservatively.
 
 
 
 No relevant conflicts of interest to declare.
