Extreme signet ring cell change in a large B-cell lymphoma of follicular origin.

We report a large B-cell lymphoma of follicular origin with extreme signet ring cell differentiation. Initially classified as follicular lymphoma on a fine needle core biopsy, the presence of cohesive sheets of extrafollicular signet ring cells triggered an excisional biopsy for further characterization. The excised lymph node revealed focal follicular hyperplasia, follicular lymphoma, and a neoplasm composed of vague nodules and sheets of large atypical cells, all of which virtually exhibited large clear intracytoplasmic vacuoles with peripheral displacement of nuclei. The tumor cells were negative for mucin and lacked immunoreactivity with pancytokeratin, but were strongly immunoreactive with CD20, BCL-2, BCL-6, and CD10 antibodies. Electron microscopy studies revealed electron-lucent vacuoles with no particular internal structure. This case is unique in that extreme signet ring cell differentiation somewhat obscured the true cytological identity of the interfollicular lymphoma and suggested alternative diagnoses.