One needs to be aware that ALCL can present some morphological and immunophenotypical characteristics mimicking metastatic carcinoma, such as sinusoidal growth pattern, loss of CD45 in half of the cases, EMA and focal cytokeratin expression, leading to a misdiagnosis of a nonhematopoietic neoplasm. The gene discussed is MUC1; the disease is anaplastic large cell lymphoma.