Aberrant expression of TTF1, p63, and cytokeratins in a diffuse large B-cell lymphoma.

Pancytokeratins and TTF-1 are used in working up carcinomas of unknown primary and p63 is expressed in many cell lineages. We present a case of a TTF-1, p63, and cytokeratins positive small round blue cell lesion presenting in a patient with enlarged right supraclavicular lymph nodes and multiple solid pulmonary nodules. The preliminary report to the clinical team was "suspicious for carcinoma." However, after a complete work up the final diagnosis of diffuse large B-cell lymphoma, nongerminal center B-cell phenotype, "double expressor," was rendered (based on Han's algorithm). This case brings up significant diagnostic dilemma as some lymphoid malignancies can morphologically mimic poorly differentiated carcinoma and stain positive for carcinoma markers. Additionally, the frequently used TTF-1 SPT23 antibody clone has strong nuclear staining in rare cases of DLBCL, which is a diagnostic pitfall. To our best knowledge this is the first reported case of DLBCL staining positive for three carcinoma markers.