the features of malignancy in effusion fluids are subtle and include ball - like three - dimensional clusters , pleomorphism , nuclear hyperchromasia , nuclear membrane irregularities , and prominence of nucleoli . cannibalism was first described by leyden in 1904 , who called them  bird's - eye cells  . in cytological preparation it is seen as a cell that is contained within another bigger cell that has a crescent - shaped nucleus . studies suggest that this peculiar property gives tumor cells a survival advantage in adverse conditions like low nutrient supply . however , only few studies have mentioned this phenomenon in fluid cytology.[57 ] we present a series of 11 cases that demonstrated tumor cell cannibalism in malignant effusion samples . the present study was a retrospective review of 100 malignant effusion cases over a time period of three years . we had group  a  of consecutive 50 cases of contiguous , local spread to pleural / ascitic fluid . in these cases , there was no apparent secondary nodal / organ parenchymal involvement present clinically or radiologically . b  constituted the remaining 50 cases which were of disseminated malignancy with secondaries in nodes / organ parenchyma in addition to the presence of pleural or ascitic fluid collection . in the period specified for inclusion of the cases , we did not have any case of mesothelioma or primary peritoneal serous carcinoma . all the 100 cases included were diagnosed cytologically on may - grnwald - giemsa and hematoxylin and eosin smears stained by standard methods . smears from all 100 cases were examined for tumor cells showing presence of another tumor cell in the cytoplasm . the number of cannibalistic cells/100 tumor cells was counted in 30 random fields at 10 magnification and confirmed by 40 magnification . we also wanted to include the count of cannibalistic cells in the primary tumor site , but unfortunately we had smears from the primary site in only six out of 11 cases . the number was not sufficient for a valid comparative study , so we did not compare the observations from the primary site cytology . details of the 11 cases demonstrating feature of cannibalism along with number of cannibalistic cells are tabulated [ table 1 ] . chi - square test and student 's t - test were applied for interpretation of the data . fifty cases of group  a  comprised 32 pleural effusion and 18 ascitic fluid samples . fifty cases of group  b  comprised 27 pleural effusion and 23 ascitic fluid samples . out of total 100 cases of malignant effusion , smears from 11 cases ( 11% ) showed the feature of cannibalism with engulfment of another cell with round to oval faded nucleus [ figure 1 ] . these 11 cases included six males and five females , with an age range of 43 to 74 years . out of 11 cases featuring the phenomenon of cannibalism , six cases ( 54% ) were of lung carcinoma , two cases ( 18% ) were of gall bladder carcinoma and one case ( 9% ) each was of liver , gastric and breast carcinoma . table 1 presents the individual case details including effusion site , primary site , secondary site involved and mean number of cannibalistic cells/100 tumor cells . b  ( 0.942.14 ) was significantly higher than in group  a  ( 0.080.39 ) { student t - test , p=0.006 } [ table 2 ] . photomicrograph showing a tumor cell with another tumor cell engulfed in the cytoplasm ( h and e , 400 ) distribution of cannibalistic cell count/100 tumor cells in group a and b in all the cases exhibiting the phenomenon of cell cannibalism , smears showed malignant cells with high - grade cytological features , poor differentiation with presence of tumor giant cells [ figure 2 ] . photomicrograph showing malignant cells with high - grade cytological features , poor differentiation with a tumor giant cell in the field ( h and e , 400 ) the cannibalistic cells were more common in group b  effusions with disseminated malignancy ( nine out of 50 cases i.e. 18% ) compared with cases of group  a  ( two out of 50 cases i.e. 4% ) . on applying the chi square test this difference was found to be statistically significant ( x 5.005 , p=0.025 ) . cannibal tumor cells have been given different names uch as  bird's - eye cells  or  signet - ring cells  . the studies related to the presence and significance of cannibalism in serous effusions are very limited.[57 ] not much attention has been paid to this cytological aspect of a tumor which actually can be of relevance in terms of staging the tumor and its aggressiveness . during evaluation of cytological smears for cannibalism , macrophages with ingested cellular debris may be present in malignant effusions as well as in inflammatory conditions , where they ingest inflammatory cells . the macrophages typically have a small vesicular nucleus with abundant pale vacuolated cytoplasm . in all our tabulated cases in the present series , tumor cells were highly anaplastic with large hyperchromatic nuclei which were easy to distinguish from that of macrophages . one should also exclude binucleated tumor cells on morphology - these cells do not show indentation in nuclei which is due to phagocytosis of the nucleus placed in its vicinity [ figure 3 ] . moreover , both the nuclei in a binucleated cell show the same intensity of hyperchromatism unlike the faded appearance of phagocytosed nuclei . photomicrograph showing binucleated tumor cell with same intensity of hyperchromasia in both the nuclei ( h and e , 400 ) search for cannibalism should be done in that part of the slide where the smear is thin and cells are evenly dispersed . areas with overlapping of cell clusters give a false positive impression of  cell within a cell  morphology . a study has quoted that the mechanism of phagocytosis by tumor cells is different from that of the macrophages and that tumor cells eat everything without distinguishing between the feeding materials . we too observed in the present series , that wherever the background had rich inflammatory component , the tumor cell had also phagocytosed the inflammatory cells in its vicinity [ figure 4 ] . photomicrograph showing tumor cell with phagocytosed inflammatory cell in its vicinity ( h and e , 400 ) a few studies[1012 ] in the past have described the feature of xeno - cannibalism , which is phagocytosis of non - self cells and a study has shown that the non - self cell most often phagocytosed is a leukocyte . in 2008 , malorni et al . , explained xeno - cannibalism as an exacerbation of self - cannibalism and a possible fruitful survival strategy for cancer cells . metastatic cells cannibalize their siblings as well as cells from the immune system , which represents a formidable opportunity for metastatic cells to survive in adverse conditions . cannibalism has been shown in breast carcinoma , giant cell carcinoma of lung , gall bladder carcinoma , malignant melanoma , endometrial stromal sarcoma , etc . in our study , , showed that melanoma cell lines derived from metastatic lesions exhibit phagocytosis whereas primary tumors did not show this phenomenon . chandrasoma p hypothesized that the ability for phagocytosis could be used as a marker for the metastatic potential of the tumor cells . studies have shown that metastatic tumor cells use cannibalism to feed in conditions of low nutrient supply and phagocytic properties offer them a survival advantage . in our series , phagocytic tumor cells were present more often in effusion samples of disseminated malignancy with secondary site involvement and all the cases displayed more prominent anaplastic cell morphology [ table 1 ] . tumor cell cannibalism is more often a feature of an aggressive tumor with anaplastic morphology and relates to its ability to metastasize .
background : cytological examination of effusion fluid is a relatively easy and quick method for the diagnosis of primary or secondary malignancy.aims:to analyze the cytological significance of cell cannibalism in malignant effusion samples.materials and methods : a retrospective review of 100 cases of malignant effusion was done . 
 these 100 cases included 50 cases of contiguous , local spread to pleural / ascitic fluid . 
 the remaining 50 cases were of disseminated malignancy . 
 effusions due to hematolymphoid malignancies were excluded . 
 smears from these cases were assessed for the presence of cell cannibalism , tumor cell within a tumor cell.results:the cannibalistic cells were more common in effusions with disseminated malignancy ( nine out of 50 cases i.e. 18% ) compared with cases of contiguous , local spread ( two out of 50 cases i.e. 4% ) . 
 chi square test showed this difference to be statistically significant ( x2 5.005 , p=0.025 ) . 
 the majority of the cases were of carcinoma lung ( 6/11 ) . 
 cytomorphologically , histiocytes displaying phagocytosis can simulate tumor cells and need to be distinguished.conclusions:presence of cell cannibalism in malignant effusions is more often an indicator of disseminated malignancy with secondaries and higher tumor stage . 
 furthermore , cannibalism may provide a reliable predictor of progression of tumor from primary to the metastatic site .