<prompt> An undifferentiated malignant tumor on immunohistochemical stain shows cytoplasmic positivity of most of the tumor cells for cytokeratin. The most probable diagnosis of the tumor isCarcinomaLymphomaSarcomaMalignant melanoma  <response>: Immunohistochemistry is used for making categorization of undifferentiated tumors. The important examples include: Cytokeratin carcinoma, Desmin Leiomyoma and Rhabdomyosarcoma and vimentin Sarcomas. 