Large anaplastic cell Ki-1 positive malignant lymphoma with peculiar endocytotic vacuoles.

Unusual intracytoplasmic inclusions are occasionally seen in some variants of malignant lymphoma. We report here a case of large anaplastic cell malignant lymphoma with peculiar vacuoles of probable endocytotic origin. Immunological findings demonstrated the characteristics of activated cells typical of a large anaplastic cell Ki-1 positive lymphoma. The tumour cells exhibited a phenotype of peripheral helper-inducer T-cells. The intracytoplasmic vacuoles were positive with the T surface marker antibodies. Ultrastructurally, these inclusions were closely related to the microvesicle-containing vacuoles reported in signet ring cell lymphomas of B or T cell lineage. The mechanism of cytoplasmic vacuole formation is discussed. An endocytotic origin is possible. The resemblance to the "capping" phenomenon in small lymphocytes is stressed.