This case is really difficult , as the morphology and tonsillar primary site is highly suggestive of mantle cell lymphoma , but immunohistochemistry does not fit .Given the CD 5 negativity I also don't believe in one of the rare CCND1 negative MCL. The conclusion by exclusion would be Marginal zone lymphoma with follicular colonization. For confirmation I would stain p27 and KI 67 ( further exclusion od MCL ,if proliferarion is low and p27 expression is high ) and kappa/lambda for secretory features . Marginal Zone lymphoma of tonsil is rare and a secondary involvement from gastric MZBL has to be considered , as we have seen a few cases showing also t (11;18).

I have little to add to Prof. Müller-Hermelink's comments, consdiering the phenotype marginal zone lymphoma is the most probable diagnosis, though the morphological pattern could also fit to mantle cell lyphoma.

I agree with Prof. Müller-Hermelink's comments and the unlikely possibility of MCL. I will sign this out as small B cell lymphoma in tonsil. I will also consider the possibility of a low grade follicular lymphoma. In areas, is clearly nodular and pretty monomorphic in appearance and I did not see the usual macrophages or other telltales of MCL. The BCL-6 is reported as negative but here is a little nuclear blush in the picture. I would recommend to add CD10, CD21 (sometimes the DRC pattern is attenuated with CD23), and CD43. The latter marker, if positive, may support a diagnosis of small B cell lymphoma other than FL. I do not appreciate much dimorphism and/or PC differentatiation (for MZL). I think kappa and lambda, perhaps MUM-1 and CD138 could be added. If everything turn out "negative" than molecular studies would be probably needed. Do you have a marrow to review?

I apologize for the delayed comment. There is little to add to the previous comments. As Attilio, I also have the impression of a slight brownish blush of the nuclei on the Bcl6 stained section. An incubation with CD10 would certainly be helpful also a BMB might help. In your proposed diagnosis you mention CLL,which is unlikely because of CD5 negativity, but it would be interesting to know if there is a lymphocytosis in the PB.

This case has been referred to the Department of Pathology, Institute of Oncology, Ljubljana (Slovenia) for second opinion and their analysis confirmed the diagnosis of marginal zone lymphoma. Thanks to all who participated in discussion regarding this case.