A case of keratin-positive acute myeloid leukemia: a possible role for cytokeratin 19 as a specific epithelial marker.

A patient with relapsed acute myelomonocytic leukemia (AML, FAB M4) developed skin infiltration by leukemic blasts. On immunochemistry, the blasts showed "bot" positive cytoplasmic staining for cytokeratins AE1/AE3 and CAM 5.2, resembling the pattern seen in Merkel cell carcinoma of skin. However, the blasts were positive for myeloid markers and negative for cytokeratin 19 and chromogranin. Aberrant immunochemical staining can lead to misdiagnosis unless a panel of antibodies of known specificity is used in tumor diagnosis, and the clinical context is taken into account. The possible role of cytokeratin 19 as a more specific marker for epithelia than keratin cocktails is discussed.