ABSTRACT
The cellincell phenomenon (CiCP) involves the incorporation of a viable cell by other cells (host cells) and includes two concepts: Emperipolesis and cell cannibalism. The former involves the incorporation of hematopoietic cells as the incorporated cells, while the latter involves cell incorporation by tumor cells as host cells. A total of 239 peritoneal cavity fluid cytology specimens were evaluated for CiCP and the number of singly detectable nuclei (SDN) were measured by examining virtual slide image files. The rates of CiCPpositive cases (RCPCs) and CiCP emergence rate (CER)/SDN were significantly higher in ascites samples than in peritoneal washing samples (P<0.0001 and P=0.0026, respectively), although the numbers of SDN were not significantly different between the groups (P=0.8063). Both the RCPCs and CER/SDN were significantly higher in tumorpositive specimens than in tumornegative specimens (P=0.0220 and P=0.0312, respectively), although the numbers of SDN were not significantly different between the samples (P=0.2471). Most of the incorporated cells were lymphocytes and the host cells were macrophages; however, the rate of neutrophil incorporation (NI) by host cells in the total CiCP cells in a sample was significantly higher in tumorpositive specimens than in tumornegative specimens (P=0.0288). NI was mainly performed via emperipolesis by macrophages, with only six examples not by macrophages observed among all CiCP samples. The threshold NI rate/total CiCP (NI/CiCP) between tumorpositive and tumornegative groups was 11.1% (P=0.0115). Using this threshold, the peripheral blood leukocyte count was significantly higher in the highNI/CiCP group than in the lowNI/CiCP group (P=0.0022). The present findings revealed novel aspects of less frequently observed CiCP in ascitic fluid cytology by utilizing combined manual and computer assisted image analysis evaluation of samples. Notably, the present study indicated the importance of increased NI as an indicator of cancerous ascites.
