P53 IMMUNOSTAINING AS A MARKER OF MALIGNANCY IN CYTOLOGIC PREPARATIONS OF BODY-FLUIDS

The accurate identification of suspicious cells in cytologic preparati ons is a common problem in diagnostic cytopathology. Recent studies ha ve shown that mutation of the p53 gene may be the most common genetic event in human malignancy. Mutation leads to altered conformation and increased half-life of the p53 protein, resulting in detectability by immunocytochemistry. The usefulness of p53 immunocytochemical staining as a marker of malignancy in the cytologic analysis of body fluids wa s investigated in the present study. One hundred fifty-four serial sam ples of body fluids submitted for cytologic diagnosis were also examin ed for p53 immunoreactivity. Of 121 cases reported as cytologically be nign, 3 (2.5%) stained positively for p53; 16 samples were cytological ly malignant, and 7 (43.7%) of these were positive for p53 (P <.001). Of those reported as suspicious but not conclusively malignant, 4 of 1 7 (23.5%) showed p53 immunoreactivity. On review, two of the three pat ients whose samples were benign cytologically yet showed positive p53 staining had histolog,ic evidence of malignancy. The third patient die d without a postmortem examination. Of the 17 cytologically suspicious cases, 16 (94.1%) were Inter proven to be malignant, and p53 was posi tive in 4 (25%). These results suggest that p53 immunostaining could b e of value as a marker of malignancy in the cytologic examination of b ody fluids. The presence of p53 immunoreactivity in cytologic samples is strongly suggestive of malignancy, though its absence does not excl ude neoplasia.