Cell cannibalism by malignant neoplastic cells: three cases in dogs and a literature review.

Cell cannibalism refers to the engulfment of cells by nonprofessional phagocytic cells. Studies in human medicine have demonstrated a relationship between the presence of cell cannibalism by neoplastic cells and a poor outcome, and have shown a positive correlation with the presence of metastasis at the time of diagnosis. The biologic significance of cell cannibalism is unknown, but it is proposed that it may represent a novel mechanism of tumor immune evasion as a survival strategy in cases of unfavorable microenvironmental conditions. This report describes clinical and morphologic features of 3 cases of dogs with malignant neoplasia in which the presence of cellular cannibalism was observed in cytologic and histologic specimens. In the 1(st) case, a dog with a primary tonsillar squamous cell carcinoma with metastasis to retropharyngeal lymph nodes had neoplastic epithelial cells engulfing neutrophils noted in cytologic examination of the lymph nodes. In the 2(nd) case, neoplastic epithelial cells were seen engulfing each other in fine-needle aspirates from a primary mammary carcinoma with lung metastasis. In the 3(rd) case, poorly differentiated neoplastic mast cells from a recurrent, metastatic grade III mast cell tumor were observed cannibalizing eosinophils. A brief review of the literature describing known cell-into-cell relationships and the possible biologic significance and mechanisms involved in this phenomenon is provided. The relationship between cell cannibalism and distant metastasis should be explored in further studies, as it may prove to be a criterion of malignancy, as it is proposed in human medicine.