Ki-1 anaplastic large-cell lymphoma in the differential diagnosis of unknown primary cancer

The importance of immunohistochemical analysis of anaplastic or undifferentiated carcinoma, especially in the setting of an unusual clinical presentation, is illustrated by two cases of metastatic undifferentiated carcinoma. Re-evaluation of pathological material resulted in a diagnosis of Ki-1 lymphoma and led to substantial alteration in therapeutic strategy and long-term outlook. The response to therapy was unusually favorable in both cases, and survival was prolonged in both. Archival pathological material was retrieved in order to perform special studies that were not originally available at the time of diagnosis, consisting of immunoperoxidase detection of hematological markers that are preserved in formalin-fixed, paraffin-embedded tissues. Both tumors were found in retrospect to actually represent anaplastic, Ki-1-positive, large-cell lymphoma. This neoplastic entity has been introduced to the oncologic literature only within the past decade. Because this neoplasm shows chemosensitivity and responsiveness similar to that of other large-cell lymphomas, we alert practitioners to consider this diagnosis in any patient who presents with an apparently metastatic undifferentiated tumor.